116 THE BACTERIOPHAGE 



In a dry state the bacteriophage is resistant for a long time. 

 A fragment of sterile filter paper is saturated with a drop of a 

 bacteriophage culture (anti-dysentery), dried in the air, and pre- 

 served in a sealed tube for six months at room temperature. After 

 this time the piece of paper is introduced into a suspension of 

 B. dysenteriae and normal, although delayed, lysis is obtained. 

 The ultramicrobes have, therefore, survived. Another ultrami- 

 crobe, that of the tobacco mosaic, has the same property. It 

 remains alive for two years in the dried leaves. It is indeed, 

 unnecessary to search for examples of bacteria as resistant as 

 the ultramicrobes. The cocco-bacillus of locusts is a non-sporu- 

 lating bacillus, but in the cadavers of locusts dead of the disease 

 which it incites in these insects (cadavers dried over sulfuric 

 acid, pulverized, and preserved in sealed tubes for three years). 

 I have shown that the cocco-bacillus remains alive and virulent, 

 for this powder, seeded into bouillon, gives normal cultures viru- 

 lent for the locust. 



SUSCEPTIBILITY TO DIFFERENT AGENTS 1 



Physical agents: Effect of temperature 



At the beginning of my experiments I stated that the tempera- 

 ture of destruction of the bacteriophage is about 65°C. Shortly 

 after this Kabeshima in an early report cited 70 to 75°C, and in 

 a later note 70°C. Very recently Gratia and Jaumain have noted 

 that the lethal temperature showed considerable variability; 

 61 or 62°C. for the lytic principle acting on the staphylococcus 

 and 65°C. for that acting on the colon bacillus. 



For testing this point I had taken as a criterion the ability or 

 inability of material subjected to different temperatures to pro- 

 duce lysis of a bacterial suspension. Moreover, this has been 

 the method adopted by the other investigators who have consid- 

 ered this question. In view of these contradictory results, the 

 effect of temperature has been reconsidered, taking as a criterion, 

 not lysis of a suspension in a fluid medium, but the action of a 

 culture on solid media, a procedure much more delicate. 



1 The experiments dealing with the effects of temperature have been 

 made in collaboration with E. Pozerski. 



