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2. That the deaths of artificially fed infants are not due solely to the use of a germ-laden milk and its resulting poisons, but that the use of an alien food creates a predisposition to infection with pathogenic bacteria which may be acquired in other ways than through the milk-as, for example, through contact or by the agency of flies.

II. A second hypothesis, held in this country some 35 years ago, and advanced anew by Meinert in 1881, is that heat itself, by its various effects upon the infant organism, must be regarded as the chief factor in the summer mortality of infants. This theory has recently gained many adherents abroad, such as Rietschel, Finkelstein, Liefmann and Lindemann, Kathe, Klose, Prausnitz, and others. I will endeavor to discuss, as briefly as possible, these hypotheses. Effects of stale or germ laden milk.-Milk is so plentifully seeded, during the course of its production and handling, with germs of all kinds, their multiplication is so favored by temperatures in excess of 60° F., and the possibilities of transmitting disease through its use are so obvious that none can deny its agency in this respect. Indeed, the accumulating literature of the epidemics of typhoid fever, the paratyphoid affections, diphtheria, scarlet fever, and septic sore throat transmitted through the agency of milk, not to mention the frequent presence of the tubercle bacillus in milk and milk products, only serve to emphasize the necessity of rigidly controlling the production and handling of this great source of food.

The most extensive investigation of recent years as to the effects of feeding different kinds of milk to infants is that of Park and Holt (49) in New York. Six groups of infants were observed, respectively fed on cheap store milk, condensed milk, milk from a central distributing station, good bottled milk, the best bottled milk, and breast milk.

During the winter but little differences in the results were noted, no matter what milk was fed. During the summer, however, the differences were striking. The infants fed on breast milk and the best bottled milk showed the best results, while these were very bad in the case of the infants fed on the condensed milk and the cheap store milk.

Rietschel, Liefmann and Lindemann, and others, however, advance the following reasons to show that the influence of cow's milk in causing summer infant mortality has been overestimated:

1. The hypothesis that the ordinary saprophytic germs of milk produce disease and death in infants is singularly lacking in experimental confirmation. The most exhaustive and complete experiments of this kind, i. e., those of Flügge (12), show that, at most, only the peptonizing bacteria in milk may have some harmful action

and are capable of exciting diarrhea when fed to dogs in large quantities.

2. Milk epidemics reported, in the literature, are mass epidemics, like other food epidemics. All the individuals, irrespective of age, who took the milk were affected. The course of these epidemics has also been quite different from that of the summer diarrhea of infants. 3. The use of sterilized milk ought to have a very great influence in reducing summer infant mortality. This does not seem to be the case. For instance, Liefmann (34) reports that infants boarded out in Halle have been provided since 1904 with sterilized milk by the municipality, yet the summer mortality among them from gastrointestinal diseases has been the same or somewhat greater than that prevailing for the rest of the city infants. Out of 384 infants supplied in this way during 1905, 1906, and 1907, 45, or about 12 per cent, died, of which number 30, or 8 per cent, died of intestinal diseases. Moreover, it has been a common clinical experience to see infants who have received nothing but the purest cow's milk, from a bacteriological standpoint, sicken with all the symptoms of typical summer diarrhea.

4. The increase in the summer mortality of infants seems to be initiated only by temperatures in excess of 24° C. While it is true that multiplication of germs in milk is greater at 30° C. than 24° C. it can not really be maintained that milk will not spoil almost as effectively at the latter temperature as at the former. Yet why should milk, spoiled at 24° C., not increase mortality, while milk spoiled at 30° does!

5. Finkelstein and Liefmann and Lindemann point out that on hot days a large part of the mortality ensues within 24 to 48 hours. Liefmann and Lindemann state, in this connection:

It is difficult to conceive how the spoiling of the milk, the infection or the intoxication of the child, the sickening, and, finally, the death can be compressed all within a single day.

While it is true, in the case of the investigation of Park and Holt, that the infants who received the cheap store milk showed the worst feeding results there are certain circumstances, noted by the investigators, which must be taken into account in weighing the conclusions.

For instance, the results of feeding with condensed milk, in which the bacteria were found to be relatively few, gave results but very little better than those obtained with the cheap store milk. Again, we are told that the store milk was boiled and subsequently kept on ice in the majority of instances. The results of the laboratory examination of numerous strains of bacteria isolated from the milk showed only one or two strains that produced diarrhea when fed to kittens.

The environment of the children was not the same, those using the store milk belonging to a poorer and needier class. It is just this

class of the population who crowd into the smaller tenement quarters with windows opening on courtyards and light wells.

Moreover, the investigators themselves state:

There seem to be many factors, but a consideration of the facts accumulated indicates that heat is the primary factor, and bacteria and their products a secondary one except when the contamination is extreme or the pathogenic organisms present.

And again:

The depressing effects of great atmospheric heat, i. e., a temperature of 90° F. or over, were very marked in all infants, no matter what their food. Those who were ill were almost invariably made worse and many who were previously well became ill.

They also indicate that proper care was, after all, the most important factor in keeping the infants well. With proper care some infants were fed successfully all summer on the cheap store milk.

That stale milk is not always deleterious to infants when the environment and care are good is shown by Rietschel's (57) experiments. Rietschel, after experimenting upon himself, fed to a series of infants cheap store milk which had previously been heated (as is the universal custom in Germany) and then allowed to stand in an open vessel for 24 hours at room temperature in the summer. The infants for the most part did very well on this diet and showed not the slightest trace of disturbance. In a few instances he had the impression that such a milk could cause more readily loose stools than a milk poor in bacteria. The milk was often turned when fed to the infants.

One further point which must be noted is that the infants which show the least increase in their death rate in summer are not the breast-fed infants, but infants who live in basements and cellars. Thus, Liefmann and Lindemann (37) inform us that in the cool part of the early summer in Berlin breast-fed infants died at the rate of 1.5 per day while in the hot part of the summer the rate was 4.5. The cellar infants died at the rate of 0.9 per day in cool weather and 2.25 per day in hot weather. Thus the death rate of the breast-fed children was increased threefold by the hot weather while that of the basement infants was only 2 times as great. This can only be explained by reason of the greater coolness of cellars and basements. Again, in the hot month of August in 1911 in Berlin, the breast-fed infants showed twice the mortality they did in the cool part of the summer, 107 dying in August, as against 51 in June.

While it can not be denied that milk, so long as it is exposed to contamination by human hands and flies, or is obtained from cows with inflammatory diseases of udder or with tuberculosis, must ever be liable to convey pathogenic germs, it would seem in view of the above statements that those who would attribute the bulk of the summer mortality of infants to stale milk take a too one-sided view of the matter and one not borne out by the facts.

The role of infections in the summer mortality of infants. The summer diarrhea of infants has presented so many of the appearances, at first sight, of a specific infectious disease, as for example, its restriction to certain streets or sections of a city and the almost explosive rise of the mortality, that much labor has been expended to discover a specific organism.

The bacteriology of summer diarrhea was first carefully studied by Escherich (8) in Europe and Booker (3) in this country. They found no definite organism associated with summer diarrhea. In 1902 and 1903 Flexner (10), Holt, Duval, and Basset (18), Wollstein (67), Gary and Stanton, Wate (62), Kendall (26), and others reported the finding of the bacillus dysenteriæ (Flexner type) in the stools of numerous infants suffering from diarrhea. It should be noted, however, that in the great majority of those cases the dejections were typically dysenteric with blood and mucus in the stools.

Within the last few years Morgan (44, 45) and his coworkers report the isolation of a motile glucose-fermenting organism, which does not attack lactose or mannit from the stools of infants suffering from diarrhea in London during the years 1904-1906. The organism was present in about 45 per cent of the cases examined and produced diarrhea when fed to laboratory animals.

There is therefore evidence that a fair proportion of the deaths of children in summer are due to specific infections, but the evidence adduced is not sufficient to explain all of them in this way. Moreover, Liefmann and Lindemann (37) have studied the course of other epidemics, such as cholera epidemics in Berlin in the summer time, in order to throw some light on this matter. They found that no effect ascribable to temperature was visible in the course of such epidemics, as their progress was quite uninfluenced by meteorological conditions, the curves exhibiting a remarkable contrast to the infant mortality curves in the same city.

Again, McLaughlin (39) has shown that where a definite source of infection from gastro-intestinal diseases exists, as, for instance, a polluted water supply, the death rate in infants from enteritis may be nearly as great in the spring as in the summer months. This has been especially true of localities which have rather cool summers.

Flies. Any hypothesis considering the summer deaths of infants as due to infections must clearly consider flies as probable or even principal carriers of the infecting organisms. The fly theory has been very carefully considered by O. II. Peters (50), who made an intensive study of the incidence of diarrhea in two sections inhabited by workmen of the city of Mansfield, England. He found no direct proof of the agency of flies in carrying summer diarrhea, and states that before this theory can be confirmed experiments of

scientific accuracy will be required, such as were used to prove the transmission of yellow fever and malaria by mosquitoes. On the other hand, he could develop no data which would render the implication of flies in the transmission of gastro-enteritis inherently impossible.

The following chart drawn from the data given by Niven (48) shows the incidence of flies as compared with the deaths from summer diarrhea in Manchester, England, by weeks. The incidence of flies was determined by counting the numbers caught weekly in traps located in various parts of the city.

It will be seen that the death rate in infants lags behind the fly curve and then increases at a much more rapid rate than the flies. These increase in arithmetrical progression while the increase in infant deaths from diarrhea is almost geometrical. The impression derived from this curve is that of an increase in flies and summer diarrhea both due to a common cause.

One other difficulty is the circumstance that Peters found, that while 32 per cent of the breast-fed infants investigated developed an attack of diarrhea during their first year, 90 per cent of the infants fed on cow's milk were affected. Yet it is difficult to conceive of an affection, spread by flies, being selective in its nature in the same age group, especially as Peters found the proportion of breast-fed and bottle-fed children receiving table food to be approximately the same. Besides this Peters found that the difference in the incidence noted above was dependent, not upon cow's milk per se but upon the circumstance of being breast-fed or not breast-fed. It can not be denied, however, that cow's milk, when kept uncovered in the home, is much exposed to infection by flies.

Finally Peters found that certain areas investigated had a much higher incidence of diarrhea than other sections showing a much greater prevalence of flies.

Effects of Heat upon Infants.

There remains now to examine the ways in which heat might damage the organism of the infant.

Heat stroke in infants.-We are all well aware that, every summer, numerous adults die in our great cities through heat stroke. As will be seen later there seem to be strong reasons for believing the infant more sensitive to heat than the adult, so there can be no ground for thinking that when adults perish, infants escape. It has been stated, in the foregoing, that hot days are accompanied by a number of deaths of infants with acute symptoms not referable to the

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