650 



GROWTH OF PHAGE AND LYSIS 



Also some of the spherical bodies showed great motility. 



(b) On Nutrient Agar Plates 



The bacteria were mixed with a 200-fold excess of phage in broth for 5 

 minutes to permit time for adsorption. Then a 0.1 cc. sample was plated 

 and observation began at 10 minutes. No changes in size or shape were 

 observable up to 18 minutes. Then first few and soon many of the bacteria 

 exhibited a variety of changes in form with parallel slow fading out. In 

 most cases the rod simply swelled to an oval or spherical shape. Sometimes 

 the swelling began at one end giving the impression of a rod attached to a 

 little sphere, gradually the rod shortened and the sphere grew until only the 

 sphere was left, which later assumed an irregular shape and finally faded out. 

 Often the swelling began in the middle at the constriction of a dividing cell 



TABLE II 



and then extended to both ends until only one sphere was visible. The 

 whole process from the inception of swelling to the attainment of a spherical 

 shape took between 2 and 10 minutes. The spheres then fade out very 

 slowly. 



Also a few minute rods are seen on the agar plate. They are never 

 lysed. Their genesis has not been observed. 



Discussion. — It is clear from the above description that lysis under the 

 influence of many external phage particles is an entirely different phe- 

 nomenon from lysis under influence of one external phage particle which 

 has grown within the bacterium to a large number. We must distinguish 

 between lysis from within and lysis from without. In the latter case ap- 

 parently the phage en masse attack the cell wall and so alter its elastic 

 properties as to permit swelling of the cell and the uptake of water. Possi- 

 bly the cell wall is actually dissolved and only the protoplasm remains and 

 swells up freely. 



64 



