PAPERS OX MEDICINE AND PUBLIC HEALTH 459 



ment. If to young cultures of Shiga bacillus ou slant 

 agar or in broth, some of the lytic principle is added, all 

 of the bacteria disappear and the medium becomes per- 

 fectly clear. After a short time, however, a growth re- 

 appears, but this is not typical of the organism in ques- 

 tion. Grattia designates these organisms by the letter R 

 for resistant, and those dissolved by S for susceptible 

 organisms. The resistant organisms can be transfen*ed 

 from generation to generation but are not ty|)ical either 

 in morphological or cultural characteristics. Old and 

 diy cultures of bacteria contain more resistant organ- 

 isms than young cultures. 



The lytic principle has been found so far only in intes- 

 tinal contents with the exception of the expeiiments of 

 Twort where he found it in vaccine virus. d'Herrelle 

 is of the opinion that all normal persons harbor the prin- 

 ciple, although in some persons it may be weak and it 

 must be activated for demonstration. A person does not 

 become ill upon infection if he has sufficient bacterioph- 

 age in his system. If the bacteriophage is weak he may 

 develop signs of the disease but recovers after the lytic 

 piinciple becomes activated. If the lytic principle does 

 not become activated or if the resistant strain of organ- 

 ism develops, the patient may not recover. Possibly 

 the production of organisms resistant to the bacterioph- 

 age is responsible for relapses in typhoid fever. d'Her- 

 relle claims that the only persons from whom he could 

 not obtain bacteriophage filtrates were those destined to 

 die. In the lower animals, as in men, the bacteriophage 

 is easy to demonstrate. It has been fotmd in horses, 

 chickens, calves, buffaloes, rabbits and other animals. 

 Very probably it is widely distributed in nature. 



The bacteria susceptible to lysis by bacteriophage are 

 mostly those from the intestinal tract, though others 

 have been described. The dysentery- bacilli, — Shiga, 

 Hiss and Flexner, — all are very susceptible. The ty]3hoid 

 group including the paratyphoid and the colon group are 

 likewise easily lysed. Bacillus proteus. Staphlococcus 

 Bacillus subtilus, the cholera organisms, and Bacillus 

 pestis have been made the subject of study. The diph- 



