284 THE BACTERIOPHAGE AND ITS BEHAVIOR 



through exposure to certain antiseptics many bacteria* become aviru- 

 lent. Inasmuch as we find that they still multiply we conclude that 

 they are not destroyed, as we would most certainly do if the bacteria were 

 infravisible. Experiment shows us that it is certainly the same for the 

 bacteriophage. Under the action of a harmful agent the virulence is 

 lost first, destruction follows later. This comment applies to all ultra- 

 viruses generally. 



In general, the vitality of bacteriophage corpuscles is very high. 

 A Shiga-bacteriophage which has been preserved in a sealed ampoule 

 for nine years has lost none of its virulence, although the number 

 of the corpuscles has diminished very considerably. When first pre- 

 pared there were 2000 million corpuscles per cubic centimeter, after 

 four years the number was reduced to only 100 million, after nine yesirs 

 to but 40 millions. From this it seems that a very great many corpus- 

 cles are destroyed during the first months. Those which remain are 

 the more resistant ones and consequently the reduction in number 

 occurs more and more slowly. With another race the number of cor- 

 puscles fell within nine years from 2400 million to 110 millions. Such 

 a diminution in numbers is not peculiar to the bacteriophage, for 

 precisely the same thing takes place with the bacteria. 



The vitality of a single bacteriophage differs according to the bacterial 

 species which has contributed to its development. Tests made upon 

 this same bacteriophage which we have just considered, after it had been 

 subject to a few passages at the expense of B. typhosus, showed that it 

 became totally inactive when held for 52 months. 



It will be recalled that we have already considered the attenuation of 

 virulence which takes place with the passage of time. It is unnecessary 

 to repeat it here. 



Confirming what has been said above, namely, that the bacteriophage 

 first becomes avirulent, and then "dies," although we can not tell when, 

 is the fact that the apparent vitality of the bacteriophage is often 

 proportionate to its virulence. But this is not a general fact; it is not 

 uniformly true as the following experiment shows.^^^ 



Typhoid patient Mor Examination of the stool was made 



at the beginning of convalescence. On August 20th, 1918, the stool 

 was treated according to the method described for securing the bacterio- 

 phage. The filtrate was distributed in 0.5 cc. amounts in suspensions 

 of the following bacteria: B. dysenteriae Shiga, B. typhosus, B. para- 



* Among others, B. anthracis, which becomes avirulent when it is cultivated at 

 a temperature of 42°C. (Pasteur) or in the presence of phenol (Roux). 



