88 II. FUNDAMENTAL STRUCTURE OF PROTOPLASM 



from the components. 



The property of preferably affecting young hosts is not confined 

 to phage, but it seems common with other viruses. For example, as is 

 well known, rapidly developing plants are liable to be readily infected 

 by virus diseases, while aged leaves having ceased growing are seldom 

 infected. The fact that the chick embryo is used for cultivation of a 

 great number of viruses may be mainly due to its juvenile character, 

 for as Woodruff and Goodpasture (99) have suggested, although many 

 viruses multiply in the chick embryo, they fail to grow in the adult 

 chicken. 



In order to obtain effectively large amounts of phage, we made a 

 small number of bacteria multiply in the culture medium with a proper 

 amount of phage. During the multiplication of bacteria in the pre- 

 sence of phage, newly produced protoplasm are imparted with the struc- 

 ture of phage. If phage is added to the culture of bacteria which 

 have already ceased to grow, usually no phage develops. Again, if 

 bacteria are spread with a small number of phage particles on agar 

 plate, a number of minute round areas, in vvhich no bacterial growth 

 is occurring are produced, which correspond to each particle present 

 at first. The phage present at first would multiply by affecting and 

 lysing the surrounding bacteria to which it is attached and the newly 

 produced phage in turn would affect the surrounding bacteria in a chain 

 reaction to increase the clearing area. The area or plaque rapidly in- 

 creases in size when bacteria are multiplying, but when their growth 

 stops the increase also comes to a halt, indicating that growing cells 

 only are affected and lysed by phage. When bacteria cease growing 

 and become aged, the phage fails to affect and to lyse them, so that 

 no further increase occurs in plaque size (100). 



Fong (101) claimed that the phage-producing ability of streptococci 

 is activated when the cocci are cultivated in a favourable environ- 

 ment for a rapid growth. Such activated cells, preserved at 5^C. in 

 Lock's solution, are able to produce phage abundantly and rapidly 

 when affected by phage, but this phage-producing capacity is quickly 

 lost when the cells are suspended in distilled water and are exposed 

 to 44°C. for 15 minutes. The activated state in this example must be 

 the "young" state, and this state can be kept unchanged at the low 

 temperature in Lock's solution, but the cells may grow "old" rapidly 

 when exposed to 44°C. in distilled water. Kopper (102) has actually 

 found certain outstanding difference between old and young cells of 

 colon bacteria. According to him, the transformation of old into young 

 cells takes place during the lag phase of growth and necessarily in- 

 volves a great number of physiological changes. The rejuvenating 

 effect was most pronounced with glucose, but also was noted with a 



