THE MECHANISM OF BACTERIOPHAGY 109 



the assumption that there be a positive chemotaxis of the bacteriophage 

 corpuscle for the susceptible bacterium, or, if one prefers (it is of no 

 consequence at the moment), of the bacteria for the corpuscle. What- 

 ever may be the nature of the force which leads to the union, the 

 attraction exists, and it is evident that anything which augments the 

 viscosity of the liquid tends to interfere with the approach of the 

 corpuscle to the bacterium, and, as a result, with its fixation. If the 

 viscosity is sufficiently high the number of corpuscles attaining fixation 

 will be so small that the phenomenon will be incapable of detection 

 macroscopicallij because of the small number of bacteria dissolved. 

 Only the proof provided by a demonstration of the multiplication of 

 the corpuscles will show that the bacteriophagy of a few organisms 

 has taken place. 



Doerr and his collaborators^^^- ^^' have attempted to draw a parallel- 

 ism between the fixation of the bacteriophage corpuscle to the bacterium 

 and the fixation of an antibody. Such a comparison is inadmissible, 

 for the characteristics of the two phenomena are entirely different. 



We know that the agglutinin content of a serum can, to all intents 

 and purposes, be completely exhausted by "saturation" with homolo- 

 gous bacteria, and that the saturation required is in direct proportion 

 to the agglutinating potency of the serum; that is to say, fewer bac- 

 terial cells are required to exhaust a weakly agglutinating serum than 

 to exhaust the same quantity of a strongly agglutinating serum. With 

 the bacteriophage the situation is exactly the reverse. In a later 

 chapter we will see that races of the bacteriophage may be isolated 

 which differ widely in their activity for a single bacterium, some being 

 weakly active, others possessing extreme activity. This difference 

 does not involve a difference in the number of corpuscles, but is due 

 rather to a difference in the activity of the corpuscles. But the partic- 

 ular point as regards fixation is precisely this, that the greater the 

 activity of the bacteriophage the fewer bacterial cells are requisite to 

 give fixation. This fact has been disclosed consistently by several 

 experiments made with both B. dysenteriae and the staphylococcus 

 and their homologous bacteriophages. 



With a bacteriophage of maximum activity, using 0.1 cc. of a sus- 

 pension containing more than 10,000 million corpuscles per cubic 

 centimeter in conjunction with 10 cc. of a bacterial suspension (250 

 million per cubic centimeter), the fixation is complete with the 

 staphylococcus, and almost complete with B. dysenteriae, within a 

 period of 20 minutes. 



