INTESTINAL BACTERIA The lively interest in the investigation of the etiology and pathology of infectious inflammations of the intestine in infancy has led to a thorough going study of the intestinal flora in the infant. After Robert Koch had delighted the scientific world by the discovery of plate culture and by the introduction of solid nutritive media, and so improved bacteriologic technique, Eseliericla wrote the first. great work on the intestinal bacteria of infancy and gave a scientific basis to the study. Further contributions WM' rapidly made by Escherich and his pupils, who concerned themselves chiefly with the relations between certain kinds of bacteria and the origin of acute digestive disturbances in infancy, and with the biological properties of bacterium coli commune. Out of the large number of more recent investigations, only those of Tissier, in the year 1900, deserve to be especially mentioned; since these enriched our knowledge, and for the first time plainly proved the great importance of anaerobic methods of culture in the study of intes tinal flora. Subsequently, the use of this method furnished valuable discoveries; and it is now indispensable for a correct judgment of the physiological conditions.
The end aimed at is to discover what forms of intestinal baeteria have to do with the causation of certain intestinal clisturbances in infancy. It is clear that on this basis the most valuable contributions may be made to the rational therapy and prophSiaxis of intestinal disease in early life. By this I mean not only those processes which Eseherich has collected under the name of ectogenous infection, but much more the endogeneous fermentations that occur in the intestinal canal, which Eischerich has called chyme-infection; and which, under the picture of an intoxication, play a predominant role in the patho genesis of aeute and chronic disturbances. The recognition. of the lat ter—that is, the endogenous infections—is much more difficult than is the recognition of the former, or ectogenous infections; for many facts are now at hand to demonstrate the frequency of ectogenous infections.
Successful investigations of these processes presupposes, naturally-, in both cases, a knowledge of the normal physiological conditions.
It is only by following this method that we can reach our goal. The chief methods in studying intestinal bacteriology are microscopic investigations of the feces in stained preparation and culture. The Weigert-Escherich stain is the best.* The intestinal flora may be studied to great advantage in the stained preparation, which allows us to recognize easily a condition varying from normal. The determination of the predominating types is possible after some experience with the microscope, so far as we have to do with the characteristic morphological types. When we have to make only a superficial examination, the preparations give valuable results which exceed in clearness and in extent those given by- culture-methods.
When the result is not clear, and w-hen we wish to study certain definite types further, microscopic investigation inust be amplified by culture. It should be emphasized that in doubtful cases culture methods are of value only when different methods of growth are used, of which the most valuable are the anaerobic method, culture on acid nutritive media, and culture on media that have been enriched (for example, on milk ancl egg albumin under aerobic and anaerobic condi tions); cultures may be made from pasteurized feces, or we may use combinations of the foregoing methods. Otherwise, one is liable to fall into the mistake of becoming elective and one-sided; and this may lead to dangerous conclusions.
A further problem is in testing the biochemical activities of iso lated bacteria with reference to the food material present in the intes tine. If we suspect the etiological importanee of a microOrganistm animal experimentation may be used to decide the question. Then, in addition to the usual methods of infection, the test of intoxication with the corresponding bacterial filtrates may lie made. Animal ex perimentation has here only a limited value, since harmless intestinal saprophytes may have a pathogenic action; whereas, animal experi ment with germs that notably call forth acute digestive disturbances may fail one completely. On the other hand, other factors, which will be mentioned later, speak much more strongly in the individual cases for the pathogenic importance of certain kinds of bacteria.