Infant Incubation – Joseph B. De Lee, 1901

Infant Incubation, with the Presentation of a New Incubator and a Description of the System at the Chicago Lying-In Hospital.

By Joseph B. De Lee, M.D., Chicago.

Professor of Obstetrics, Northwestern University Medical School;
Attending Obstetrician of Mercy, Wesley and Provident Hospitals,
and Obstetrician of Chicago Lying-In Hospital and Dispensary.
Chicago Medical Society, December 1901.

Published in the Chicago Medical Recorder 22:22-40, 1902

In the middle ages premature infants were wrapped in the skin of a sheep, with the wool on, or put in a jar of feathers. Later they were enveloped in cotton. Sterne [1], in the middle of the eighteenth century, relates how the child of a physician was raised by the “same artifice that one used to make chickens hatch in Egypt. He put his son in an oven, properly constructed, heated regularly, the temperature of which was regulated by suitable instruments.” Nothing came of this suggestion.

In 1857 Denuce [2] described a double walled bath tub, with water in the interspace, for the rearing of feeble infants. In 1866 Crede [3], of Leipzig, used an identical contrivance, although he did not publish it until 1884. In 1880 Tarnier had Odile Martin, a poultry raiser of the Jardin des Plantes, construct an infant incubator on the plan of a chicken incubator. It was installed in the Maternité and could hold several children.

Individual incubators were subsequently constructed, of which that of Auvard is the best of that period. It consists of an oblong, wooden box heated by cans of water, with an opening for air at the bottom, a vent at the top containing a wheel to indicate the movement of the air, and a glass, sliding cover. The child is supported on a shelf and a wet sponge is hung near by to keep up the moisture. Nearly all the incubators in this country are modifications of this form of apparatus.

The objections to all of these instruments are that they are of wood, and therefore harbor infection; they are clumsy; they have unhandy heating methods; e.g., hot water bottles or cans that are to be emptied and filled frequently; they have no automatic heat regulation, little provision for moisture, poor ventilation and no provision for fresh, uncontaminated air, so that often the air in the incubator, owing to the high temperature, is worse than that outside. Therefore, infection of the child occurs, and many infants are better off out than in the box.

Some of these instruments are still on the market. They serve but one purpose — to keep the infant warm, and that may be accomplished as well with a shoe box and hot water bottles. Rotch [4] has constructed an incubator on wheels, containing a scale for weighing the infant and a very complicated system of ventilation. It has not attained general use. Winckel [5] (see cut No. 1) has constructed a permanent bath in which the child floats, this to avoid the rapid evaporation and imitate more closely the liquor amnii. The bath ought to be placed in an incubator.

Some incubators are open at the top like a box, others at the front; some are heated by hot water bottles, some by hot water systems connected with a boiler outside, some by hot air, others by steam; none, that I know of, by electricity, though the last would seem a good way. The best model is, I think the system Lion. Paul Altmann and Gebrüder Müncke, of Berlin; Kny Scheerer, of New York, and perhaps others make instruments after this model, varying in the details. I think it is the best form in which the apparatus can be made. The incubator which I present this evening is of this shape, but differs from all in the ventilating and heating systems. I have spent much time and labor for two years in perfecting it, and feel that it is now in condition to be recommended to the profession.

There are four main problems in incubator work. First, and easiest, the heating apparatus; second, the ventilation, of considerable difficulty, but of most importance; third, moisture, of the most difficulty and of considerable importance; fourth, portability and simplicity, neither of which can be obtained, unless at the expense of the ventilation.

In addition to these the incubator must be aseptic; that is, easily disinfected; must be handy to work with and not exorbitant in price. To obtain all these qualities in one portable incubator is very difficult.

The body of the incubator is a box twenty nine inches high, twenty two inches deep and twenty inches wide; it has two compartments — a lower, containing a water pan, and an upper for the infant, which lies on a cotton mattress swinging in a basket. The two compartments are connected by air flues only. There are doors at the front, through which the infant is handled, and a sliding door at the side, through which it is watched and fed. The lower front is removable for sterilizing and cleaning.

The Heating System.

The heating system consists of a water pan (G) inside the box near its floor, connected with a boiler (R) on the right, outside the chamber. This is in all respects similar to any hot water heating system. The premature infant requires a warm, moist atmosphere, of a definite tension, and also a sure and constant amount of radiant heat. The air must be 86° to 93° F., the bed must be 94° to 100° F., and these must vary proportionately as the incubator is set at one or the other degrees of temperature. These figures were obtained by thermometric observations. The radiant heat is supplied from the top of the pan (G) and controlled by the distance between it and the bed (J). The air is heated by the under surface of the pan, as we shall see later. Both must be automatically regulated, which is obtained thus: In the upper right half of the chamber are three biconvexed hollow discs (O) containing ethyl chloride; these expand and contract with heat and cold. The slight motion thus obtained is multiplied by a system of levers (P) thirty times, and in this way the cover (Q) of the air flue of the hot water boiler (R) is raised and lowered. When the cover is raised the heat escapes, the water cools, the temperature in the incubator sinks. When the incubator grows too cool, the discs contract, the cover falls, the hot air is confined, the water is heated and then the temperature is raised. This regulator can be set at any degree from 70° to 100° F.

The difficulties encountered with the heating apparatus were, first, to get a thermoregulator that would work. This one is the result of some experiment, much study, and the investigation of the instruments in the practice of poultry raisers. Mercury and gas regulators are not practical for infant incubation; metallic coils did not function regularly, or for any length of time, and electric thermostats were a complete failure. Second, the gas pressure varied throughout the day. This is obviated by attaching a gas pressure regulator to the burner; before we did this the work of preventing irregularities of the heat production and loss incident to the height of the flame had all to be borne by the thermoregulator; now this is not the case. Third, changes in the temperature of the room. A cold draught will cool the incubator before the regulator can supply the heat. This is obviated with this instrument, by protecting it from such chilling. In a larger system which we are going to install the incubators will be placed in a room, the temperature of which is to be even. Fourth, extreme changes of temperature outside. Of course, no one would expect any thermoregulator to equalize the extremes of our Chicago temperature. A change of 50 degrees is not impossible here, and to anticipate these variations the hospital is supplied with the daily weather forecast, and a thermometer is placed outside the nursery window, which the nurse consults, and regulates the admission of cold air to the incubator by a damper (B). Even without such attention, this incubator took care of a change of 47 degrees (see chart i.). For below zero weather we will install a preparatory warming chamber for the air. To show how perfectly this thermoregulator functionates, I have had hourly observations made during periods of two days (see chart ii.). The incubator was set at 90° F., and in two days did not vary more than three degrees; that is, from 88° to 91°, while the outside temperature, given by the official weather bureau, varied 16 degrees, and the wind veered around the points of the compass.*

The Ventilation.

This has given us a great deal of trouble, and those familiar with the difficulties attending the natural ventilation of houses will appreciate the obstacles met here. The change in the room temperature, the extremes of outside temperature, the faulty construction of houses, the opening and closing of doors, the dry days, the wet, muggy days, the high and low barometric pressure, but especially the direction of the wind and its strength have prepared for us no end of problems.

Without going into these difficulties, I will describe the system as it stands today, practically perfect. The air is taken from a low point outside, where there is some sunlight, and led to the incubator by a three inch pipe (A); it passes through a cotton filter (C) at the side of the lower chamber, passes beneath the water pan, under which it is spread by a curved plate (F); it is heated, and therefore rises through the flues (H) at the side of the upper chamber. It circulates downward around the infant (IJ), is collected under the bed (K), drawing off the odors from the child, and ascends through the flue (L) at the head, escaping through a chimney (M) from the top of the apparatus. A glass cylinder placed in this flue allows one to see the ventilator, or anemoscope (N), which indicates the current of air. Three feet above this chimney is a four inch air exhaust flue with an eight inch funnel. This creates a current from the floor of the nursery toward the ceiling, and is to check over strong down draughts into the incubator. It also carries out odors from the incubator. For hot, damp, muggy days, it may be necessary to aid the ventilation of the apparatus by modification of the intake of air from the outside, which problem will give little difficulty. The current through the incubator must be the gentlest possible, to give the infant enough air and yet not chill it with a draught. It is remarkable how sensitive these air currents are to even delicate fluctuations without. An incubator system cannot be operated successfully unless the air be taken fresh from outside. The air of hospitals is almost never good, and if heated is still worse for a delicate infant.

The question of moisture is still being investigated. In the first place we lack a good hygrometer. We use the coil instrument standardized with Mason’s. Secondly, we lack knowledge of the amount of moisture an infant needs and of the amount it can tolerate when the air is at a high temperature. In ordinary room temperature of 65° to 70°, the relative humidity varies from 55 to 65 per cent. The amount of saturated aqueous vapor in a given space varies with the temperature, being small with hot air and large with cold. Thus the difficulty when the air of the incubator is heated up to 90° to 92° F. The relative humidity is reduced to 10 or 12 per cent unless artificial moisture is applied. This is done by passing the cold air over a wet screen, and, if necessary, by a small pan of hot water placed under the infant. The percentage of relative humidity best suited to infants is the subject of our study, and a report will be rendered later. At present we try to hold it between 35 and 50 per cent.

A machine that will accomplish these functions is necessarily bulky, complicated and unwieldy to transport. A specially trained nurse is required to manage it, but such nurses are needed for the baby. The children had better, then, be sent to the hospital, which is usually advisable also for many economic reasons.

The claim is made for this apparatus that it is an incubator built on scientific lines, and not a mere warm box. After the best regulator is once adjusted it needs no further attention. The ventilation is even and certain, and the moisture, with ordinary watchfulness, is held in normal degree. Like every important instrument it requires intelligent attention and care.

The Indications for the Incubator.

At first the couveuse was used only for premature and congenitally feeble infants, but its success with these soon caused the indications to be extended, until the instrument was abused — being employed for nearly all the ills of early infancy. Then the error was recognized, and recently Delestre [6] has stated that the couveuse should only be used for infants with subnormal temperature, and that as soon as the child has a temperature that remains at 98.6° F. it should be put in its cradle. This, to my mind, is also an error. The incubator has more extensive use than this; that is, the incubator herein described. For the Auvard incubators built on that plan, the statement may hold, for these incubators are little more than warm boxes and do nothing but heat the baby.

The first and most important indication is prematurity. We must consider as premature, infants born sooner than three weeks before term, those that weigh less than five and a half pounds and are shorter than forty six cm. The signs of prematurity need not be discussed here, save to say that children may be born near term and still be small, and children of a shorter period of pregnancy may be larger and heavier. Also, a child may weigh four and a half pounds and present stronger evidence of prematurity than one of three and a half pounds, if the latter has been longer in the uterus.

All children that weigh less than five pounds, or are born with the evidences of prematurity, should be put at once in the incubator. They may not need to stay there more than two to five days, but the first hours are especially dangerous, and they need the protection the apparatus affords. Children weighing as little as two pounds and four ounces have been saved by the incubator; the smallest we saved weighed two pounds and twelve ounces.

Induced labors especially indicate the incubator, because in addition to prematurity there is the shock of the interference. As a matter of fact, such children do not do as well as those where labor comes on spontaneously.

Second, congenital feebleness. Infants of fair size are sometimes born weak and with poor resistance, shown by subnormal temperature, slight cyanosis, tendency to edema or sclerema. They should be treated as premature. With acquired feebleness from wasting disease, the author has had no incubator experience. The instrument, as at present perfected, I believe deserves trial here.

Third, edema. Premature infants are not seldom subject to a general edema, beginning at the feet. It may be unattended with cyanosis or with urinary changes. Its cause is unknown. The incubator is the quickest way to relieve the condition.

Fourth, cyanosis, with or without edema, due to feeble circulation, is very common with small infants, and sometimes present with those at full term. The warm, moistened, oxygenated air of the couveuse does wonders in these cases.

Fifth, subnormal temperature, from any cause.

Sixth, after difficult operative deliveries, the baby is often in a condition of shock, which, to my mind, is as common as asphyxia. Violent efforts to revive it should be limited to a minimum, and the infant placed as soon as possible in the incubator. It need stay here but one to four days. This is true of full term children, but especially true of premature.

Seventh, hemorrhagic diathesis. Melena neonatorum is an indication for the incubator; likewise all congenital hemorrhagic manifestations; e.g., hemophilia, multiple hemorrhages, morbus maculosus Werlhofii. The writer has had two cases where the effect was marked — one of melena with eight profuse hemorrhages and one with hemorrhages from the nose, mouth, into the skin and with a spleen that came to the pelvis. Both recovered.

Eighth, sclerema neonatorum. There are two kinds, one an edema with cyanosis and subnormal temperature, common in premature infants, a second with hardening of the fat, perhaps later with some edema, likewise with subnormal temperature, usually due to wasting diseases and the last stages of the same. For the first condition the incubator achieves brilliant results; for the latter it is useful, but not so much may be expected.

The incubator has been used for the treatment of collapse from any cause, secondary, asphyxia or atelectasis, respiratory affections, as an adjunct in the treatment of syphilis, for chronic enteritis and in the arthrepsia of wasting diseases. The effects in many cases have been favorable, and further trial is indicated.

On one point the greatest stress is to be laid. The premature or debile infant must be placed in the incubator at the earliest possible moment after birth. Every minute’s exposure to outside influences lessens the chances of life. To minimize the danger of exposure during the travel to the hospital, the Chicago Lying-In Hospital has an ambulance incubator constructed on the principles of Auvard’s (see cut.)

Care to be Given Incubator Infants.

The premature or debile infant requires infinitely greater care and watchfulness than the healthy newborn. It is more liable to sepsis, to digestive and respiratory complications, to ophthalmia, and, in general, exhibits a weakness against all noxious influences. The writer cannot here enter into a discussion of the various methods of treatment, but will describe the course he instituted at the Lying-In Hospital.

The incubator. The ventilation need not be altered for each infant. Just enough to keep air changing is right, and the nurse attends to this by operating the damper in the fresh air flue. In winter less air is needed, in summer the valve is wide open. The temperature of the incubator is usually set at 89° F. If the infant is very premature, or has a very subnormal temperature, one may begin with 91° or 92°, though we have found 89° meets with most requirements. If the child is larger, or when it is ready to leave the couveuse, the temperature is set 86°, 84°, and 82°, successively. Then the slide is opened to accustom it to the external air, and then the heat is turned on only at night. If the child’s temperature goes below 90° it almost always dies.

The moisture is likewise regulated, according to the needs of the child. Thirty five to fifty degrees [sic] is a proper range. The nurse has to attend to this, which is done by offering a greater or less surface in the moisture box, or by putting water in the moisture pan. The punier the infant, the more moisture needed; otherwise, the little body dries up, the beginning of which is noticed by dryness of the lips and tongue. The higher the temperature of the incubator, the more difficult is the attainment of a regular and normal relative humidity. The incubator should always be kept closed, being opened only to remove and replace the infant; otherwise the thermoregulator will provide more heat and disturb the accuracy of the temperature regulation.

The dress of incubator infants should be all of wool, except the diaper. Soft, thin, wool flannel, a simple bag tied around the neck and left long enough so as to be doubled over the body, a woolen binder and the diaper, complete the apparel. The baby is covered with a thin, wool flannel blanket, leaving only the face exposed. This dress allows changes to be made quickly, and gives freedom of motion so necessary to prevent hypostasis.

The diet is equal in importance to the incubator. After much experience, I must say that without mothers’ milk, it is almost impossible to raise a premature infant — certainly, to be a healthy one. For this reason, an incubator station, to be successful, must be in connection with a lying in hospital. I have given up all attempts with artificial feeding, and get mothers’ milk at any trouble and expense. The next best is mixed feeding. One must regulate the frequency and the amounts of the feedings, by the size and vigor of the infant. For the smallest, twenty to thirty drops of a two-thirds diluted mothers’ milk, are given every forty minutes to an hour, later, two drams every hour, larger children in proportion. Planchon [7] gives the following figures, which we have found to agree with ours.

Some children require more, others less, and the amounts vary day and hour. One must not overfeed, because of digestive disturbances, fermentations and indigestion, and, too, regurgitation causing choking and cyanosis, which may be fatal. One must give sufficient, and begin within a few hours after birth to avoid weakness from hunger which sometimes shows itself in attacks of collapse or cyanosis. The amount at each feeding must be recorded, and if the baby nurses at the breast great exactness must be practiced to be assured it has obtained food.

Method of Feeding. If the infant can suck and swallow, the food is given with a tiny nipple on a little vial. If the child cannot suck, it may be given with a medicine dropper, either by mouth or through the nose. Gavage is the practice of feeding with a stomach tube. The catheter is passed into the stomach and food poured in slowly. The tube is then quickly withdrawn, the infant being held quiet for a few minutes. If the child can be taken to the breast, it is fed by means of a teterelle. The mother draws the milk into the bulb of the glass, and then allows it to flow into the mouth of the child. One should see that the infant has plenty of water, especially in hot weather, because evaporation is rapid and such children have a relatively large surface and thin skin. With tiny infants, for the first week, feeding is done in the incubator, through the side window. Later they are fed in a warm nursery.

The Bath. The incubator infant at first needs no baths. It should be anointed daily with benzoinated lard. Dried discharges on the face and buttocks may need a little water and soap. After the infant is ten days old, it may be bathed in water at 103° F., in a hot room. The nose, ears, mouth and buttocks must be kept scrupulously clean, which is not easy, because of the smallness and tenderness of the parts. No force dare be used, because injuries invite infection.

Daily general massage and passive motions must be practiced, with extreme gentleness at first, but later the infant must be accustomed to external conditions. The infant is weighed daily and the temperature taken morning and evening, per rectum, and oftener, if the nurse suspects unusual variation. The child should not be disturbed, except for giving it needed attention, and should be placed alternately on its two sides.

Removal from the apparatus, depends on the age of the infant and its rate of growth. As a general rule, when the temperature remains normal for days, when the child is about four and one fourth to four and one half pounds in weight, we remove it to its cradle. This varies, of course, so the length of stay is from five days to four weeks. There is no haste in removing the child; it will thrive better in the apparatus, having less to contend with. Operative cases are removed when they have recovered from the shock of the delivery. It has occurred to the writer that an incubator on a large scale would be useful in treating shock in adults. Success in incubator work depends as much on the nursing as on the apparatus. Without a conscientious, selfsacrificing, intelligent and trained set of nurses, the best system will give poor results.

Diseases of Incubator Infants.

It is manifestly impossible to review the entire field of these affections, as the premature infant may have all the diseases of full term children. Several affections, however, are peculiarly severe in the premature infant.

First. Sepsis occurs in a great many, and usually comes from the bowel, either as an intoxication or a general infection. Broncho-pneumonia is another fatal complication, and is not usually suspected because the infant shows such feeble signs of life. A subnormal temperature and cyanosis, with loss of weight, are sometimes the only symptoms, and they might be explained by other things.

Second. Ophthalmia neonatorum, when it occurs, takes on a very virulent form, perhaps due to the warm air making conditions favorable to the growth of bacteria. It is particularly difficult to treat because of the weakness of the infant and the smallness of the part. General sepsis may occur from the eye, and in all ways, the prognosis is bad.

Third. An affection which has been observed not infrequently at the incubator station of the Maternité in Paris, but with which we have had no experience, is an ulcerative rhinopharyngitis, due to decomposition of food which the baby regurgitates into the nares. Profuse discharge, soon purulent, ulceration of the mucous membrane even to the bone, with the development of saddle nose similar to that of syphilis, are reported [8]. Sometimes this causes a broncho-pneumonia and general sepsis. The treatment is one of local cleanliness and antisepsis, which, however, is not easy to practice.

Fourth. Attacks of syncope are not unusual with premature infants. They simply forget to breath. Cyanosis soon becomes marked, and unless properly treated, death ensues. The child is limp and there is no attempt to respire. Post mortem, no mechanical cause for the death is found. There is another form of cyanosis which comes on suddenly, too, where the infant chokes, becomes cyanotic, and may die of asphyxia unless the cause be removed. This cause may be an overloaded stomach, especially with artificial feeding, when vomiting relieves the condition; second, an undigested curd regurgitates into the pharynx, and the infant is too weak to remove it. This shows the importance of having a light incubator and watching the baby. Finally, these attacks may be due to a developmental anomaly of the stomach or of the chest.

The treatment of the first condition — syncope — is stimulating. First see that there is free ventilation in the incubator and that the infant has not a subnormal temperature. A hot bath with a little wine or mustard in it should be given. The nourishment must be certain, but not too free. A little coffee or whiskey may be given, and inhalations of oxygen. These are of signal benefit. The treatment of the second condition consists of removing the obstruction, regulation of the diet, less and more dilute mothers’ milk and the usual curative methods of asphyxia post partum.

Fifth. Atelectasis pulmonum. This affection is not infrequent with premature infants, and is due to several causes. Syphilis, as a white hepatization, or catarrhal pneumonia; developmental anomalies, e.g., diaphragmatic hernia, insufficient development of the lungs, compression of the trachea by a struma, injury to the respiratory center from compression, and, most often, to insufficient primary inflation of the lungs. The child is reddish blue, unconscious, grunts or moans with each expiration; later, the extremities become almost black and edematous. The child dies usually, in four to forty hours, intense cyanosis and jaundice being present toward the last. At each inspiration, one can see the chest sink in at the base.

The treatment consists in obtaining sufficient inflation of the lungs, and then the incubator. One must not be misled by the child’s breathing, or even by its crying lustily; if each expiration is attended by a grunt or moan, and if the normal pink, or dusky red, does not come into the skin, the child is in danger. Its lungs are atelectatic and must be filled out, or the infant is lost. The best way to obtain this is to put a catheter into the trachea and blow air into the lungs — then Schultze’s swingings. The other methods of artificial respiration are not efficient. The infant should be made to cry every two hours. Oxygen has a marked effect in these cases, but will not save them unless the lungs are finally inflated.

There is now no doubt of the incubator saving infant life, especially premature children, and the percentage of these is not small. Vallin [9] reported to the Academy of Medicine in Paris, November 12, 1895, as follows: “We are compelled to consider premature, all infants weighing less than 2500 grams (5 pounds, 7 ounces), and they number 15 to 30 per cent.” In London in 1886, 1,033 premature infants died, in 1896, 2,534.

In the Paris Maternité the infant mortality since the introduction of incubators has been reduced one half [10].

Statistics of Various Incubator Stations
Percentage of Children Saved

At the Chicago Lying-In Hospital 28 babies have been placed in the incubator in two years. Any premature infant that has a spark of life, is given the benefit of every means we have to save it. Of these 28, 8 died in a few hours, usually being frozen or in convulsions on arrival at the hospital; 3 had hemorrhagic diathesis; 2 died of atelectasis pulmonum; 1 lived 4 days, and 14 were reared and discharged well. Of the 14 that died, 2 were in the sixth month, 4 in the seventh month, and 8 in the eighth month. Of the 17 children that could be saved, 14 were saved.

The later results are also of interest. Ahlfeld [12] found that 90 per cent of infants brought prematurely by artificial induction of labor, were alive and well at the end of the dangerous first year. Voorhees (l. c.) shows relatively as favorable results. Paul Bar [13] cites the case of an infant of six months’ pregnancy, weighing two pounds and ten ounces, born in 1894. At the age of four years she weighed thirty five and a half pounds and was thirty nine inches high, a bright, intelligent little girl. I present here a photograph of an infant born six months and fourteen days after conception. She weighed three and a half pounds at birth, and now is a normal child in every particular.

Capuron [14] tells of the case of Furtuni Liceti, born in the fifth month, who lived to be twenty four years old. Moore [15] gives a trustworthy account of an infant that at birth weighed one and a half pounds and was nine inches long; at fifteen months this infant weighed eighteen pounds and was healthy. Spaeth [16] says he has known a child of six months’ pregnancy, surpass in eventual development his brothers born at term, and, to cap all, Victor Hugo was a premature infant, so weak and puny that the accoucheur said the child could not live. In his own words, Victor Hugo says he “came into the world colorless, sightless, voiceless and so poor a weakling, that all despaired of him, save his mother.” It was six weeks before he was able to travel [17].

Therefore, it cannot be said that the effort to save these infants is not worth making. On the contrary, every protection should be thrown around their delicate lives.

3632 Prairie Avenue.

Bibliography.

1. Budin. Tristam Shandy, Lecous de Clinique Obstetricale, 1889, p. 259.

2. Denuce. Jour. de Med. de Bordeaux, Decembre, 1857.

3. Credé. Arch. f. Gyn. No. XXIV., S. 121.

4. Rotch. Arch of Pediatrics, 1893.

5. Winckel. Centralblatt f. Gyn. 1882, Seite I, 19. 38.

6. Delestre. These de Paris, Juin 1901.

7. Planchon. L’Obstetrique, 1901, Sept., p. 418.

8. Henry. Rev. mens. de mal de L’Enfance, 1898, p. 143.

9. Vallin. London Lancet, 1897, I. p. 1490.

10. Auvard. Arch. de Toc., 1883.

11. Vorhees. Arch. of Pediatrics. 1900. p. 331.

12. Ahlfeld. Centrb. f. Gyn. 1901.

13. Bar, Paul. Lecons de Path. Obst. Paris, 1900.

14. Gould. “Anomalies and Curiousities of Medicine.” p. 72.

15. Moore. Ibidem.

16. Spaeth. Ibidem.

17. Marzials, F. T. Life of Victor Hugo, in “Great Writers.” Edited by E. S. Robertson, London, 1888.

18. Arnaud. La sala incubatrice. Torino Locatelli. 1901.

19. Ch. Maygrier. Deux Statistiques. L’Obstetrique. Nov., 1901. p. 481.