RESISTANCE OF BACTERIA 183 



races of the Shiga-bacteriophage capable of effecting a complete dissolu- 

 tion of normal suspensions and with such a race it is not necessary to 

 filter the dissolved suspension through a candle to insure that the 

 medium remain clear and sterile indefinitely. With such races bacteri- 

 ophagy can be continued throughout an unlimited series without filtra- 

 tion between the successive passages. After a process of selection it is 

 the same for the Staphylo-bacteriophage described by Gratia as race H, 

 but in order to obtain this result it is necessary that bacteriophagy take 

 place at a temperature of 32°C. and that the bouillon have a pH greater 

 than 7.5. If these conditions are not satisfied a number of the suspen- 

 sions, after a complete clearing, again become cloudy after an interval 

 of time, and it is of interest that the number of suspensions to become 

 turbid increases as the conditions become more divergent from the 

 optimum. 



The following experiments were carried out with Staphylo-bacterio- 

 phage, race H. Normal suspensions, containing 250 million cocci per 

 cubic centimeter, prepared from a 24-hour agar culture were used. Ten 

 cubic centimeters of the suspension were inoculated with 0.001 cc. of the 

 bacteriophage. Each of the experiments comprised 24 tubes, each 

 containing 10 cc, subjected to the same treatment at the same time. 



Experiments 1 to 5 illustrate the effect of temperature. In all of 

 these the reaction of the bouillon was 7.8. 



1. Temperature, 25°C. After 32 hours bacteriophagy was complete 

 in all 24 tubes. After 7 days, at 25°C., the 24 suspensions were limpid. 

 After 2 months at laboratory temperature the 24 suspensions remained 

 unchanged, — perfectly clear. 



2. Temperature, 31°C. After 19 hours bacteriophagy was complete 

 in the 24 tubes. After 7 days, at 31°C. the 24 suspensions were clear. 

 After 2 months at laboratory temperature they still remained clear. 



3. Temperature, 36°C. After 18 hours bacteriophagy was complete 

 in the 24 tubes. After 72 hours at 36°C. the 24 suspensions were limpid. 

 After 4 days at 36°C., 23 were limpid; one was cloudy. After 5 days at 

 36°C., 22 were limpid and 2 were cloudy. After 7 days at 36°C. the 

 result was the same. After 2 months at room temperature the results 

 still remained the same; 22 tubes being clear, 2 being cloudy. 



4. Temperature, 40°C. After 18 hours bacteriophagy was complete 

 in all 24 tubes. After 28 hours, 11 tubes were clear, 13 were cloudy. 

 After 72 hours all 24 tubes were cloudy. 



5. Temperature, 31°C. After 24 hours all 24 of the suspensions were 

 clear. After 6 days they still remained clear. At this time 20 of the 



