1 64 PROTOPLASMIC ACTION AND NERVOUS ACTION 



understood. Perhaps the clearest light on the problem 

 has been afforded by the phenomena of salt-antagonism. 

 These have shown definitely, at least in certain cases, 

 that structural changes in those parts of the cell which 

 are most directly exposed to the action of the solution 

 (plasma membranes and other surface-structures like 

 cilia) are the primary condition of the effects produced. 

 The toxic and other effects are secondary consequences 

 of these structural changes. The physical condition of 

 the structural colloids — state of subdivision, of hydration, 

 of electrical polarization, etc. — is changed by the action 

 of the salt, with corresponding changes in the properties 

 of the cell-structure itself and of the chemical and other 

 activities controlled by it. In many cases the injurious 

 action of the pure salt-solution (NaCl) is referable to a 

 destruction of the normal semi-permeabiHty of the plasma 

 membrane; this effect, if not soon reversed, involves 

 chemical and other disorganization followed by death. 

 Any condition preventing or retarding the alterative 

 action on the membrane, such as the presence of an 

 antagonistic salt or non- electrolyte (narcotic), has 

 accordingly a protective or "anti-toxic" action.^ These 

 general conditions are well illustrated in a simple marine 

 organism much used in experimental work at Woods 

 Hole, the larva of the annelid Arenicola cristata. This 

 is a segmented trochophore larva about one-third of 

 a mihimeter in length, having pigmented body cells 

 and swimming by a combination of muscular and 

 ciliary movements. When placed in pure isotonic 



' Cf. the discussion in my paper on antagonism between salts and 

 anaesthetics, American Journal of Physiology, XXXI (1913), 255; cf. 

 pp. 2 75ff. 



