VIRULENCE OF THE BACTERIOPHAGE 167 



in spite of the fact that it was preserved in sealed ampoules. Various 

 observations made in the course of my studies contribute additional data 

 upon this question of spontaneous attenuation. 



One race of the Shiga-bacteriophage, originally very virulent, has been 

 held for a period of 9 years in a sealed tube, and throughout this period 

 it has remained almost as active as it was at the beginning. The sole 

 change consisted in the number of corpuscles, which diminished from 

 2400 million to 110 million, but despite this reduction in numbers those 

 which survived retained their virulence without change and this viru- 

 lence was equal to that of corpuscles having the same origin but which 

 had undergone, throughout this time, between 1500 and 2000 passages. 

 Other races of Shiga-bacteriophage from various sources, but all very 

 virulent, hkewise maintained their activity unchanged during periods of 

 3 to 5 years. A very active Staphylo-bacteriophage, held in a sealed 

 ampoule, retained its potency completely for a period of 3 years. A 

 second race, somewhat less virulent, was attenuated after 4 years to 

 such an extent that it was lost in the second passage when an attempt 

 was made to restore its virulence. Two very active races of Coli- 

 bacteriophage maintained their virulence for 6 years. Three races 

 which originally showed a strong virulence, although somewhat less 

 than that of the two races just mentioned, were dead or totally avirulent 

 after the same interval of time.* 



A Barbone-bacteriophage of high virulence when sealed up in an 

 ampoule had lost a large part of its virulence after 11 months, but with 

 3 passages the virulence was restored. After 26 months this particular 

 race was dead or completely avirulent in some of the ampoules whereas 

 in others it was still present, although attenuated to such a degree that 

 it was lost during the first passage. 



A Cholera-bacteriophage tested after it had been preserved for 8 

 months was completely avirulent. During the attempt at rejuvenation 

 a few minute plaques could be seen in the first passage, but with the 

 second passage it disappeared. 



A Plague-bacteriophage (of rodent origin) retained almost all of 

 its activity throughout a period of 26 months. Another race (of human 

 origin), somewhat less virulent at the beginning, was very markedly 

 attenuated in the same length of time. After 40 months the first race 

 was still very virulent; the second was dead or avirulent. 



* The bacteriophage can be recognized only through its virulence for a given 

 bacterium. Consequently it is not possible to tell whether the bacteriophage as 

 such has disappeared or whether it has become avirulent, for in either case it 

 would not be possible to disclose its presence. 



