CYTOMORPHOSIS IN BACTERIA 143 



in the organism. As an extreme example of this viewpoint, we may 

 quote Child, who maintains that what we call protoplasm of cells 

 is but a relatively inert framework about which the chemical pro- 

 cesses concerned with growth and age and death take place. He 

 states that, "According to this view the colloid substratum and the 

 morphologic structure of the organism represent, so to speak, the 

 sediment of the metabolic process." 



Also the widespread occurrence of dedifferentiation in cells, not 

 generally admitted at the time of Minot's publications, now seems 

 to be generally accepted. This is especially evident in lower forms 

 of life, in the process of regeneration after excision of a part or in 

 the reconstitution of individuals from excised parts. It also seems 

 to have been established beyond question in the case of tissue cul- 

 tures. Here conditions are quite comparable with those which ob- 

 tain in cultures of bacteria. Cells left remaining in plasma tend to 

 differentiate and finally undergo senescence and death; while if 

 continually transferred to fresh plasma they may be continually 

 maintained in a relatively undifferentiated condition. Similarly, as 

 was shown in Chapter IV, bacteria left in the same medium tend 

 to revert to the mature form as indicated by shorter length of cells, 

 but if continually transferred to fresh agar remain in the embryonic 

 form characterized by long cells. 



Child has studied the phenomena of growth and death from a 

 physiologic standpoint, and has discovered that the physiologic age 

 of an organism or tissue can be determined by its relative suscepti- 

 bility to certain poisons, there being a correlation between the degree 

 of susceptibility and the degree of physiologic youth of the cells 

 or organisms investigated. Not only is there a difference in the 

 susceptibility between young and old individuals, but it can be 

 shown that there is a difference in susceptibility between growing 

 and resting parts of an organism. Regenerating pieces of planarian 

 worms are physiologically ydunger than the same tissues when a 

 part of the whole animal; and similarly small pieces as measured 

 by their susceptibility have a higher metabolic rate than large ones. 

 This is very interesting from our standpoint, because, as has been 

 previously related, Sherman and Albus have discovered that cultures 

 of bacteria are more susceptible to various injurious agents, as heat 



