130 PHYSICAL CHEMISTRY 



ions on the rate of pulsations of medusae, but the anomalous 

 action of Ca" was again apparent. Perhaps the explanation of 

 this lies in the assumption that the effect of the ions on pulsations 

 is the summation of their effect on various tissue and cell struc- 

 tures, and that the sensitiveness of these structures is different 

 for the same ion, the ions standing in no constant ratio in this 

 regard. This is illustrated by the fact that Mg" is a strong 

 •depressant of muscular contraction whereas Mayer (1915, 1916) 

 has shown it to be without effect on nerve conduction rate. 



The All-or-N one Law 



If the action current (which we may assume is the excitation 

 wave itself) rests on so mechanical a basis as has been set forth 

 it may seem difficult to picture different gradations of excitation. 

 Much evidence is being accumulated by physiologists to show 

 that no gradations of excitation exist so far as the single cell is 

 concerned, but that all excitations are maximal (Bayliss, 1915 a). 

 This is called the all-or-none law. A weak nerve impulse is ex- 

 plained as an impulse in which only a few fibers take part and 

 a maximal impulse one in which all of the fibers take part; and 

 the same principle holds for muscle. Tonic impulses are due 

 to a succession of excitations involving a minute proportion of 

 the fibers at any one time, and producing a fibrillation in the 

 muscle that gives it tone. Such a tonic excitation continues to 

 affect a veratrinized nerve muscle preparation for some time 

 after a single stimulus is applied, thus retarding the relaxation 

 of the muscle. The peculiar series of action currents after 

 veratrin poisoning may be detected with the string galvanometer 

 (Lodholz, 1913). Such a delicate instrument is not necessary 

 in case of the electric organ, however, which shows the same 

 behavior toward veratrin (Winterstein, 1910 iii (2) 185). 



The all-or-none law removes a series of objections which might 

 be raised against a purely physicochemical hypothesis of excita- 

 tion. It is the present purpose merely to call attention to this 

 fact. For a discussion of the evidence in support of the law see 

 Bayliss's Physiology. 



Absorption and Secretion 

 The fact that the intestine may absorb a hypertonic solution 

 introduced into its lumen has for a long time been the cause of 



