276 THE BACTERIOPHAGE AND ITS BEHAVIOR 



branes of different permeabilities, that the ultraviruses of rabies, of 

 vaccinia, of encephaHtis lethargica, and the bacteriophage all have, 

 within the limits of the method of measurement, the same diameter. 

 When one of the four passes through a membrane they all pass, when one 

 is retained, all are held back. 



Experiment seems to show that the bacteriophage corpuscle under- 

 goes a shrinking with ageing. As a matter of fact, when comparative 

 filtrations through membranes of approximately the same porosity are 

 made it is found that corpuscles which are 20 days or more old pass 

 through membranes which hold back young corpuscles. An experiment 

 bearing on this point may be cited. It has been repeated on two differ- 

 ent occasions, and the results of both tests were alike. 



A suspension of Shiga-bacteriophage filtered immediately after the 

 completion of bacteriophagy, was mixed with an equal quantity of a 

 suspension of the Staphylo-bacteriophage which had not been filtered 

 through a candle until one month after bacteriophagy had taken place. 

 At the same time a second mixture was prepared of equal parts of a 

 suspension of Staphylo-bacteriophage filtered through a candle imme- 

 diately after bacteriophagy, and a suspension of Shiga-bacteriophage, 

 filtered 20 days after the dissolution. Two series of collodion sacs 

 were prepared, the sacs of each series progressing from very tight sacs 

 to those more porous. Into the sacs of one series the first mixture was 

 introduced, the second mixture being placed in the second series. The 

 materials of all the sacs were dialyzed against bouillon, a pressure of 3 

 to 4 cm. of bouillon being established in each sac. 



After 48 hours the external bouillon was examined to ascertain which, 

 if any, of the bacteriophages had passed through. These tests showed 

 the following: 



Series 1. With the four sacs that were least porous there was no 

 passage. Through sac No. 5 the Staphylo-bacteriophage corpuscles 

 had passed, unmixed with the Shiga-bacteriophage. From sac No. 6 

 a great many Staphylo-bacteriophage corpuscles had passed and also 

 a very few Shiga-bacteriophage corpuscles, the ratio being 100:7. 

 With the two most porous sacs the corpuscles of the two races of bac- 

 teriophage had passed in essentially the same proportions. 



Series 2. Nothing had passed through the first 5 sacs, that is through 

 those sacs which were least porous. Through sac No. 6 a great many 

 Shiga-bacteriophage corpuscles had passed as well as a very few 

 Staphylo-bacteriophage corpuscles, the ratio being 100:2. Through 

 sacs Nos. 7 and 8, both races had passed. 



