THE BIOLOGICAL ACTIVITIES OF BACTERIA 71 



through many generations that he was dealing with a living ultra- 

 microscopic organism which fed upon" the living bacteria and, there- 

 fore, spoke of it as a " bacteriophage. ' ' 



A curious and important phase of the work was that this lytic 

 principle was to some extent specific in that it acted only upon 

 a single or a few closely related microorganisms. 



In subsequent notes D'Herelle reported that he had produced 

 such bacteriophage lytic principles against dysentery bacilli of 

 Shiga and Flexner and "Y" type, against typhoid, paratyphoid 

 "A" and "B," against enteritidis, hog cholera, coli, prodigiosus and 

 some other Gram-negative bacilli. Without wishing to detail all 

 his investigations, the principles may be summarized as follows: 

 In all cases the lytic principle was filtrable and could be carried 

 on from generation to generation as above described. Young ac- 

 tively growing cultures were necessary to transmit the lytic activity 

 in series; it could not be transmitted by dead bacteria. The lytic 

 principle and the bacilli were not killed by the same temperature. 

 Whereas the Shiga bacillus and other organisms worked with were 

 destroyed at or about 50 C., the lytic principle resisted tempera- 

 tures up to 65. The lytic principle isolated from the feces might 

 at first be feeble, but was considerably augmented in potency by 

 cultures in series. Certain cultures were from the beginning en- 

 dowed with bacteriolytic power against two or more different species 

 and preserved this action against these species for a long time if 

 cultivated only on one of them. For example, he isolated an active 

 principle against the Shiga and typhoid bacillus from the stool of 

 a dysentery convalescent. After a series of 1,000 passages, the 

 successive cultures always being carried along on Shiga emulsions, 

 there was still marked lytic action against typhoid bacilli. He never 

 isolated two strains that were exactly alike. The intensity of action 

 differed and one strain would from the beginning show lytic power 

 against a number of intestinal bacilli. Others, again, would be 

 active against only a single species. Another, again, might attack 

 only two, the Flexner bacillus and paratyphoid "B." 



D'Herelle was quite definitely convinced that he was dealing 

 with an ultra-microscopic organism which perhaps was capable of 

 developing in the intestines of man and animals at the expense of 

 various bacteria, and could then be cultivated out of the body by 

 the method he had developed. This was the reason for the name 

 he applied to those principles, "bacteriophage," which implied that 



