ii6 BACTERIAL ASSOCIATIONS 



similar adaptive alterations are to be expected in the growth in mixed cultures. How 

 fundamental these changes may be is not as yet determined, and the study of dis- 

 sociation should help us in our knowledge of the possible range which may occur in 

 the bacteria as they are grouped by our present-day rather crude methods of classifi- 

 cation. Bacteria may be forced to metabolize substances in a different way under 

 certain environmental conditions than they would under other conditions, and this 

 induced, but not necessarily new, function may become fairly well fixed by repetitions 

 as a characteristic of the organism. In looking over the examples already given there 

 are many instances to be found of such occurrences apparently brought out by bacterial 

 association. LommeP has given an important instance of this. By growing a non- 

 saccharose fermenting B. coli with B. typhosus, B. paratyphosiis, or the Shiga bacillus 

 after some twenty passages it took on the function of actively attacking saccharose. 

 She does not say how long this induced activity continued under non-associative con- 

 ditions, as only a plate and agar slant intervened between the tests. She has, however, 

 shown that certain B. coli lost their ability to ferment lactose by continued growth on 

 malachite-green media and that this loss remained constant for some, but not for all 

 strains after fifty-six transfers on plain agar. 



OTHER APPLICATIONS 



Passing by numerous other well-known examples of bacterial association such as 

 that of B. fusijormis and Spirocheta vincenti, which Rukawischnikoff^ and others 

 look upon as only stages in the growth cycle, and many mixed infections occurring in 

 man and animals, I would give the interesting use made of this phenomenon by WoU- 

 man.-' He used B. coli as an indicator to determine proteolysis by bacteria previously 

 grown in horse serum, egg albumin, and similar substances through its ability, after 

 such primary growths, to produce indol. He thus tested B. anthracis, B. subtilis, 

 Staphylococcus aureus, and B. putrificus and later^ determined the proteolytic activity 

 of streptococci by this method. Thompson^ was enabled by a symbiotic method with 

 B. proteus to isolate an anaerobic B. acwe-like organism from cultures of B. tuber- 

 culosis and suggested its relationship with the latter. I believe it might well have been 

 present as a contaminant and brought to light by this technique. 



DISCUSSION 



Before closing I would call attention to the necessity of determining more care- 

 fully than has been done the intimate metabolism of the bacteria we are studying and 

 the environmental requirements necessary for the manifestation of their manifold 

 characteristics, before any attempt is made to explain the phenomena I have re- 

 viewed, those of bacterial association, or the active metabolism shown by the bac- 

 teriophage. It is well known that d'Herelle^ considers the bacteriophage a living, sub- 



' Lommel, J.: Compt. rend. Soc. de bioL, 95, 711, 714. 1926. 

 ' Rukawischnikoff, E.: Ccntralbl.f. BaktcrioL, I, Orig., 100, 218. 1526. 

 ^ WoUman, E.: ConipL rend. Soc. de bioL, 82, 1263. 1919. 

 ^Wollman, E.: ibid., 87, 1138. 1922. 

 5 Thompson, E. T.: Lancet, 2, 1S6. 1920. 



•^d'Herelle, F.: The Bacteriophage. 1922; Immunily in Natural Infectious Disease. 1924; The 

 Bacteriophage and Its Behavior. 1926. Translated by G. H. Smith. WilHams & Wilkins. 



