PROTOPLASM AS A PHYSICAL SYSTEM 57 



within the limits of a single cell without mutual inter- 

 ference; different metabolic processes are thus localized* 

 a necessary condition for a definite "chemical organiza- 

 tion" of the cell. 



It is well known that when living protoplasm is 

 acted upon by cytolytic agents or heat (40°) or is altered 

 mechanically or osmotically (i.e., by hypertonic or 

 hypotonic media) beyond a certain degree, chemical 

 changes are induced in it which are absent or inappreci- 

 able under normal conditions. These changes are as- 

 sociated with profound structural alteration, as shown 

 by coagulation of the cell-proteins, changes of permea- 

 bility and water content, and loss of the normal tensile 

 and other mechanical properties of the protoplasm. 

 Thus in muscle, and probably in most other cells, lactic 

 acid is formed in large quantity; in many cells autolytic 

 changes are initiated; in oxidase-containing fruits and 

 tubers (apple, potato) the browning reaction occurs; 

 and in many cases (muscle) there is a marked temporary 

 increase in the output of CO2. Of special interest is 

 the fact that these changes are associated with a loss 

 of the normal semi-permeability of the plasma mem- 

 branes, coincidently with a loss of the characteristic 

 water-immiscibility of the protoplasm as a whole; hence 

 disintegration by diffusion processes follows rapidly. 

 These effects are such as might be expected to result 

 from a breakdown of the normal partitioned structure 

 of the system. Materials which during life are kept 

 apart by the interposition of films are thus enabled to 

 interact; hence (as already cited) autolysis is accelerated 

 by cytolytic compounds like chloroform. For a similar 

 reason the minuter structural elements — which normally 



