372 PROTOPLASMIC ACTION AND NERVOUS ACTION 



According to this conception the anaphylactic 

 reaction of smooth muscle cells becomes an example 

 of specific chemical stimulation, dependent on the 

 presence of specific substances (presumably protein) in 

 the surface layer of the reacting cell; these substances 

 react with substances of corresponding or complementary 

 configuration in the environment, and hence furnish 

 the conditions for a highly selective and specific type 

 of response. Presumably other forms of specific chemical 

 sensitivity are also to be referred to the presence of 

 specific chemical compounds in the surface-films of the 

 reacting cells. Such a conception renders clearer the 

 general nature of the relation between the special 

 chemical sensitivity exhibited by a particular species of 

 cell and its specific chemical organization. Any change 

 in the chemical constitution or physical state of the 

 plasma membrane must influence irritability and hence 

 the other properties or activities controlled by this 

 region of the cell. 



OTHER INDICATIONS OF THE CONNECTION BETWEEN 

 INCREASE or PERMEABILITY AND STIMULATION 



Certain instances of stimulation-effects which are 

 associated with an evident increase of surface- 

 permeabihty have already been cited. Perhaps the 

 clearest instance of a direct dependence of a normal 

 functional response upon a sudden increase of permea- 

 bility is seen in the osmotic motor mechanisms of plants, 

 such as the Venus' flytrap and the sensitive plant. 

 In the latter plant, Mimosa pudica, the leaves are kept 

 in the normal expanded and upright position by turgid 

 or water-distended masses of parenchyma cells (pulvini) 



