RESISTANCE OF BACTERIA 185 



Once bacteriophagy is completed with the suspensions perfectly clear; 

 those tubes which are to give a secondary culture can not be distin- 

 guished macroscopically or microscopically in any way from those which 

 are to remain clear indefinitely. Transfers to bouillon and on to agar of 

 l)acteriophaged suspensions in which a secondary culture is to develop 

 later remain sterile up to the time that the secondary culture appears. 

 This does not often occur until 5 or 6 days after the dissolution, some- 

 times even later. 



A suspension of Shiga bacilh, containing 250 milHon bacilh per cubic 

 centimeter, is inoculated with 0.001 cc. of a culture of the bacteriophage. 

 Normal bacteriophagy takes place in 5 hours, with the medium perfectly 

 limpid. The dissolved suspension is planted on agar and in bouillon 

 1, 2, 3, 4, 5, 6, and 7 days after the dissolution is complete. All of the 

 plantings remain sterile. On the eighth day the dissolved suspension 

 is slightly clouded. On the ninth day a drop is introduced into broth 

 and drops are spread over 3 tubes of agar. Two of the agar tubes 

 remain sterile, the third shows 4 small colonies. The broth tube gives 

 an agglutinated, sedimented culture.^^^ 



The following experiments show that the number of secondary cul- 

 tures to develop diminishes as the virulence of the bacteriophage is 

 increased. The most potent race of the bacteriophage which I have yet 

 isolated (these experiments were carried out in 1918) was combined with 

 2 strains of the Shiga bacillus. One of these bacterial strains has been for 

 a long time under artificial cultivation, being used by the Pasteur Insti- 

 tute for the inoculation of horses in the production of anti-dysentery 

 serum (type strain) . The other was recently isolated from the stool of 

 a patient with dysentery (strain Jerv.). 



(A) Twelve tubes of the suspension of the type strain of the Shiga 

 bacillus are each inoculated with 0.001 cc. of a culture of the bacterio- 

 phage. This latter has been carried on for a great number of genera- 

 tions always at the expense of a single bacihary strain. In all twelve 

 tubes dissolution is perfect, with complete clearing in four hours. After 

 three days at 37°C. one of the tubes is slightly cloudy, the others are 

 clear. (Five other experiments, each consisting of 12 tubes, with the 

 same race of the bacteriophage and the same bacihus give the follow- 

 ing results: — tubes showing secondary cultures in each set, 0, 2, 0, 3 

 and 1. There develop, then, 7 secondary cultures in the 60 tubes, or 12 

 per cent.) 



(B) Twelve tubes of suspension were prepared with the strain Jerv., 

 a strain with which the bacteriophage in question had never been in 



