This is even more true of the intestines of the artificially fed infant. The microscopic picture, which is characterized by great richness in variety and form, indicates this definitely. The study of intestinal bacteria does not require so much the complete and systematic dis covery of the bacteria present as the selecting from among the large number of saprophytic ancl transitory inhabitants of the infant's intes tine those forms that are of importance for physiological processes in the intestine. The predominanee of the colon group and the presence of bacteria having proteolytic action is especially marked in the feces of the artificially fed infants. The bacteria in the meconium, originally described, were previously considered accidental inhabitants of the intestines, only demonstrable in the stools during the meconium period before they had been driven out by the germs taken in with the food; but my latest investigations have shown that large number of the so called meconium bacteria arc identical with the organisms subsequently found in milk stools. The difference between them is simply external, affecting the form of growth; since the meconium furnishes an mn favorable medium for the growth of the entering germs, and compels the formation of spores and permanent types. Thus we find already present in meeonium the bacillus bifidus, the bacillus coli communis, the butyric-acid bacillus, the above described "little-head" bacterium, and the bacillus putrificus—all forms of bacteria that are later found in the milk stool and continue to vegetate in the intestines after that period. The meconium prevents the indiscriminate migration of ubiq uitous germs into the intestine of the new born, and allows only those bacteria to enter that have a specific biological affinity to the intes tines and their contents. Thus the specific infection of the intestines with the obligatory bacteria of the intestine is accomplished even in the first days of life. With the appearance of the first stools after nursing, the bifidus multiplies rapidly. When artificial nourishment is instituted, on the other hand, the colon bacteria predominate; and all other forms become of little importance.
3. The occurrence of a changed vegetation in the feces is, under normal conditions, not so much the result of new bacteria introduced with the food as the expression of an elective, one-sided multiplication of one or the other type of bacteria already present in the intestine. This, also, would explain the alteration of the intestinal flora as the result of a decided change in artificial feeding. A diet rich in starch favors the development of the saccharolytes: food rich in albumin, the vege tation of the proteolytes. The possibility therefore exists of restraining intestinal putrefaction by giving starch plentifully (Escherich).
I have demonstrated, by investigating bacteriologically, imme diately after death various portions of the intestine of breast-fecl children showing no intestinal diseas,e, that the different forms of bacteria are not distributed haphazard in the intestines but that their distribution follows certain laws. Especially- remarkable is the fact that the upper parts of the intestine, particularly the small intestine, are nearly free from germs. The amount of bacteria does not become considerable until the eecum is reached: and from there, it increases steadily. Whereas the bacteria of the colon group predominate in the duodenum and the lower part of the ileum, the bifidus vegetation suddenly appears in the eccum, and in the colon already predominates over all other types of bacteria. The flora of the cecum, on the contrary, offers a more or less polyntorphous picture. This is due to the frequent occur rence of the butyric-acid bacilli and other spore-carrying anaerobes in this section of the intestine. From these results it follows that the investigation of the feces in the stool gives no satisfactory information concerning the higher portions of the intestine, and that we must dis tinguish between the ideas: fecal bacteria, and intestinal bacteria.
The quantity of bacteria excreted with the Feces is enormous. From 20 to 30 per cent,. of the total nitrogen in the stool of the breast-fed infant is due to bacteria. The majority of the microbes excreted are probably- dead, but our information on this subject is generally defec tive, because the investigators did not always consider the anarobic and acidophile forms.
The biochemical activity of normal intestinal bacteria in the infant expresses itself chiefly in decomposition of the food constituents and the food residue, of the nature of fermentation and putrefaction. The nitrogen withdrawn from the food remnants and built up into bacteria is, in all probability, more than off-set by the absorption of dead microbes in soluble form by the intestine.
The assistance that intestinal bacteria furnish to the process of digestion can be only small, so far as concerns the taking up of the food stuffs and their transformation into directly absorbable substances. Nevertheless, the assumption that intestinal bacteria, in a hitherto unexplained fashion, directly or indirectly take part in the process of digestion and favorably influence nutrition, cannot be altogether re jected. Experiments have demonstrated that newborn animals brought up with sterile surroundings and on sterile food remain deeidedly back ward in development as compared with control-animals, and show the influence that the intestinal flora exert upon nutrition. In fact, some animals could not be kept alive without intestinal bacteria (Schottelins, O. Metschnikoff, Moro, Nuttall, and Thicrfelder).
Fermentation and putrefaction are antagonistic processes; that is, we cannot have putrefaction in a medium that is undergoing fer mentation. Both processes are caused by the presence of specific bac teria. The energetic ferment-producing bacteria. predominate in the infant's intestine (especially the obligatory milk-feces bacteria of lische rich and the large group of anaerobic butyric-acid bacilli). These ener getic ferment-producing bacteria prodominate very much over the genuine bacteria of putrefaction (especially the group of anaerobic putrefactive butyric-acid bacilli, bacillus putrificus con; the spore carrying type of gas-phlegmon bacillus, etc.). For this reason, acid fermentation prevails in the normal infant's intestines, and under physiological conditions (that is, when the child is nursed), putrefactive processes may be entirely prevented. The acid products of metabolism of intestinal bacteria have an exciting influence on intestinal peristalsis, and are essentially aided by- the presence of intestinal gases.
Intestinal gases arise primarily from the life-activity of intestinal bacteria, and their constant presenee in the intestine is probably not without importanee. Intestinal gases play an important part in the topography of the abdominal contents, and regulate intestinal peristalsis. They keep the intestinal lumen open for the entrance of food, and the mingling of the latter with gases favors its transportation. The surface of the mucous membrane, without any doubt, becomes considerably greater from the distention of the intestines with gases. The villi are unfolded and the coiled vessels in the intestinal wall become dilated and stretehed. This favors absorption and makes the circulation of the blood easier.
A very important role of normal intestinal bacteria is their ability to protect the intestine to a marked degree against the invasion of organized foes, through the products of their metabolism. The correctness of this VICW is demonstrated by our daily experience of the uniformity of the intestinal flora, a.s well as the fact that milk-feces and fecal culture-media check the growth of microbes that are foreign to the intestinal tract.