134 THE BACTERIOPHAGE AND ITS BEHAVIOR 



in stained preparations, whatever the magnification, microorganisms 

 other than B. dysenteriae. 



We have already stated that corroded or partially destroyed bac- 

 teria, such as would necessarily occur if the dissolution was made from 

 the outside inward, are never seen. Destruction always takes place 

 by rupture. This is true not only for the dysentery bacillus but for 

 all bacteria which undergo bacteriophagy. Furthermore, for all 

 species the ''microscopic" picture of the phenomenon is the same. 



Examination under the ultramicroscope clearly indicates, then, that 

 the bacteriophage corpuscles multiply within the interior of the bac- 

 terial cell, and it is possible that the very fine refractile granules, so 

 small as to approach the limits of visibility with the dark-field, ob- 

 served within the interior of the bacteria in process of being bacterio- 

 phaged represent these corpuscles. These granules are still visible 

 in the floccules which float in the liquid for some time after the rupture 

 of the bacteria. They cease to be visible when the floccules are com- 

 pletely dissolved. 



This part of the discussion is, evidently, only an hypothesis, for as 

 yet it is impossible to affirm that these fine corpuscles may not be due 

 to changes in the bacteria. Nevertheless, the "coincidences" argue in 

 favor of their bacteriophage nature. 



The fact that these granules are only visible when within the bacteria 

 and that they cease to be so when they are free in the medium is not a 

 basic objection to this view. That the bacteriophage is of corpuscular 

 nature is undoubtedly true; indeed the fact is no longer questioned.* 

 We will see that its dimensions are essentially the same as those of the 

 protein micella. Its diameter has been determined by Prausnitz 

 in one way and by von Angerer in another, and both methods agree 

 in placing the size at between 20 and 30 millicrons. If it is not visible 

 under the ultramicroscope it is most certainly because of its strong 

 power of imbibition; the same thing that prevents the protein micella from 

 being visible,! namely, because their refractile indices are essentially 

 the same as that of the Hquid in which they are suspended. But the 

 index of refraction of the bacterium is certainly different from that of 

 the liquid medium, as is shown by the fact that they are perfectly 

 visible without staining. It follows therefore that the index of refrac- 



* Doerr is the only author who is not quite convinced upon this point, although 

 he does not deny it. 



f Metallic micella, even those whose diameter is much less, are visible because 

 the index of refraction differs from that of the liquid. 



