376 PROTOPLASMIC ACTION AND NERVOUS ACTION 



nescent cell which responds to stimulation by a flash 

 of light, all three substances are apparently present and 

 available, but during the resting state they are prevented 

 from uniting by the presence of protoplasmic films or 

 partitions; when as a result of stimulation these parti- 

 tions are temporarily broken down, chemical union and 

 light-production result. Further analysis of the condi- 

 tions of luminescence in irritable cells will no doubt 

 throw much light upon the general nature of stimulation 

 processes. 



Harvey^ has recently made some simple and striking 

 experiments on plant tissues, giving further indication 

 that in living cells under normal conditions chemical 

 reactions are frequently prevented or restricted by the 

 presence of protoplasmic partitions or membranes 

 impermeable to the interacting substances. The oxidase 

 reactions which cause the browning of potato, apple, or 

 similar tissues are examples. If a potato is cut in the 

 presence of oxygen, the browning occurs only at the cut 

 surface; even in pure oxygen under high pressure, the 

 interior tissue remains unchanged. This absence of 

 effect cannot be referred to an impermeability to oxygen, 

 since all of the physiological and chemical evidence 

 indicates that living protoplasm is freely penetrated by 

 this gas. The oxidase and the chromogen are in some 

 way prevented from uniting while the tissue is living. 

 If, however, it is exposed for a few minutes to chloroform 

 vapor, the browning extends rapidly throughout the 

 whole mass. Apparently the effect of the chloroform 

 is to break down the protoplasmic partitions which 

 normally prevent free union of the compounds. Destruc- 



^ E. N. Harvey, Jour. Gen. Physiol., V (1922), 215. 



