A few years ago it was thought necessary to boil the milk one-half to three-quarters of an hour, but. more recent experiments have shown that a shorter boiling has nearly the same effect, while the milk under goes fewer changes. For instance, the writer, according to the cleanli ness of the milk, recommends a boiling of from two to five minutes in winter time and of from five to ten minutes in summer time. The boil ing causes certain changes in the milk, which are described in detail on page 316. The most important are a change or coagulation of the pro teids, a destruction of the alexines and ferments, change of the salts, etc. It is easy to conceive that these changes are not without impor tance in the suitability of the milk as food for infants. It is nearly cer tain that the sterilization of the milk is of influence in the causation of infantile scurvy. Occasionally, delicate infants begin to thrive when they receive raw milk, while previously under otherwise equal condi tions the feeding with boiled milk had not been successful. Parallel experiments conducted with mother's milk have shown that the infants did better on raw milk than on boiled milk (Moro). We may mention here the severe intestinal and fatal disease observed in newhoro calves which ore raised On sterilized cow's milk, while calves raised on raw milk do not suffer from it. At present, certain general disturbances observed in infants raised on sterilized milk are attributed to the ster ilization of the milk. The assumption that the native properties of the milk are lost in the boiling may lend a certain degree of probability to this idea.
Heating the milk for a longer time to 6.5° to 75° C. (119° to 167° F.) has a similar effect on the bacteria as has germs are destroyed, while the changes of the milk are less profound. This method of pasteurization has been ITIW:ti Cd1V aml warmly recommended of late, and special pieces of apparatus have been designed to enable the pasteurization at home. There is a danrer that all parts of the milk do not reach the necessary temperature. if only a small quantity remains below this, as may easily happen if a skin is formed, the bacteria are not destroyed, and again infect the rest of the milk in a short time. Special precautions have to be taken to avoid such occurrences. as. for instance, the use of stirring or shakinp. devices. If the temperature ex ceeds a certain limit the desired advantages are lost. Special care is necessary in keeping and using pasteurized milk. The less dangerous bacteria can easily be recognized by the changes they produce in the taste and odor of the milk. but the touch more dangerous peptonizing bacteria which survive can only he detected ith much greater diffi culty. Occasionally it may be of advantage to combine sterilization and pasteurization. The milk is kept boiling for two to three minutes and is then placed for fifteen minutes on the hot oven. Thus the milk is aradu-dlv cooled to GO° to 70° C. (110° to 15ti° F.). Then it has to be cooled to 10° to 15° C. (50° to 59° F.) as rapidly as possible.
The addition of disinfecting substances has been tried. in order to render the milk as free from germs as possible without essentially alter ing its properties. Thus. Behring again recommended the addition of formalin which had formerly been used for this purpose. The addition
of preservatives in sufficient dilution may not he of danger to the in fant, aside from other serious objections against their use in milk. Seiffert tried to sterilize the milk by exposure to ultraviolet rays. but experiments on a larger scale for practical purposes have not been con ducted. With reference to other experiments see p. 333.
Moderate boiling is to be regarded as the surest, most convenient, and cheapest method of freeing the milk from bacteria or reducing their number, without altering the milk too much. Such a procedure is neces sitated by the manner in which the milk is obtained. It could be avoided by putting the infants directly to the udder of the animals furnishing the milk. This method would have the additional advantage that the infants would be forced to do some work in suckling.
Even where good cow's milk was used and the food was prepared rationally, the results never were as good as with breast-milk. Biedert explained this fact as due to the different proteid content of these two kinds of milk. He claimed that the cow's casein and therefore the cows milk is less digestible than is human milk. This assumption, that the cows casein is more difficult to digest, has been accepted widely. But more recently its fallacy has been proved, particularly through the in vestigations of Ileubner and the school of Breslau, inasmuch as it has been shown that the resorption of cow's casein is not inferior to that of human casein. But the possibility is not excluded that the cow's milk proteid may act in an injurious manner on the intestines. A new ex planation for this possibility came forward recently, to which Biedert calls attention. The biochemical investigations have shown that the proteids of the cow's milk are heterologous for the infant, while those of the human milk are homologous (heterologous, or foreign to the species; homologous, or not foreign to the species). Hamburger drew far-reaching conclusions from this, as it is known that each organism strives to preserve strictly the peculiarities of its species with regard to its cells and body juices, since it reacts against a proteid of a foreign species introduced into its tissues as against a poison. It is the function of the intestines to supply the organism with homologous proteid, and this function is accomplished through the decomposition of the heterol ogous proteid,—the digestion,—and then through the reconstruction, —the assimilation. These processes may be regarded to a certain ex tent as a kind of detoxification. The heterologous proteid constitutes the physiological pabulum for the digestive cells in the adult, but it acts as an injury to those of the newborn infant. In contradistinction to the adult, the detoxification of heterologous proteid is not a physiological function of the infant, and in this manner Hamburger explains the injurious effect of cow's milk. Escherich attributes the difficulty of artificial feeding partially to the quantitatively insufficient power of assitnulation with regard to cow's proteid. At present we cannot judge with sufficient exactness how far these conceptions agree with the actual facts.