VIRULENCE OF THE BACTERIOPHAGE 145 



last active dilution to be 10~^. Working with these dilutions in a 

 volume of 5 cc, they removed 4 cc. from the last active dilution and 

 distributed it as follows: 



a. One cubic centimeter into a sterile tube. 



b. One cubic centimeter into a tube with 10 cc. of bouillon. 



c. One cubic centimeter into 100 cc. of bouillon. 



d. One cubic centimeter into 1000 cc. of bouillon. 



The four specimens were then seeded with a culture of B. coli. Bac- 

 teriophagy took place in all of them. It seemed strange to Gratia and 

 de Kruif that bacteriophagy should occur in the flask containing 1000 

 cubic centimeters, where the ''concentration of the lytic principle," ac- 

 cording to their expression, was only 10~^^ when it did not take place in 

 the 10"^ dilution when working with 5 cc. quantities. Inasmuch as a 

 long time before this I had shown that bacteriophagy takes place if but 

 a single corpuscle is added to a bacterial suspension,and that bacterial 

 dissolution does not occur if this corpuscle is lacking (a condition re- 

 calhng the "all-or-none law"), the results of Gratia and de Kruif should 

 not have appeared so unusual. 



Incidentally, the term "concentration" as apphed by these authors 

 to the bacteriophage principle is an expression without significance, 

 and it can only lead to confusion when used in this connection. 



Werthemann-'^" has proposed a scheme of notation designed to express 

 the "concentration" of the bacteriophage principle. According to this 

 scheme "concentration" is indicated by the exponent of the last active 

 dilution. For example, in the experiment of Gratia and de Kruif 

 already mentioned, the CoU-bacteriophage would be termed active up 

 to the concentration 1-10~^, or eL8 according to the scale of Werthe- 

 mann. Since concentration is not the dominating factor in the phe- 

 nomenon of bacteriophagy one might well question the significance 

 of such a notation. Not only does it aggravate the defects inherent 

 in the method of titration by dilution, but it adds a false conception. 

 To ascertain how invalid such a method is I would recommend that 

 those who employ the procedure repeat the experiment of Gratia. 



Beckerich and Hauduroy" have proposed the following method. 

 Each of a series of tubes receives 1 cc. of a young culture of the sus- 

 ceptible bacterium. The bacteriophage suspension whose activity is 

 to be measured is then added in decreasing quantities — ^perhaps 1:3 in 

 the first tube, 1:5 in the next, up to a dilution equal to 3 parts 

 in 10,000,000,000. A portion of the contents of each tube is spread 

 over an agar plate, while the remainder is retained in the tube to indi- 

 cate what takes place in a fluid medium. 



