230 THE BIOPHYSICAL PROBLEM OF NERVE CONDUCTION 



and most fruitful of these versions were proposed by Blair* [1932] in the 

 form of a physicomathematical theory, and by Hill [1936] as a chemical 

 wave theory of excitation and conduction in nerves. 



Although the two theories start with somewhat different assumptions, 

 the generalization of them by Offner [1937], by Young [1937], and by 

 Katz [1939] shows that the fundamental time-intensity relations of 

 nerve fibers are identical for all type of stimulating current; on the whole, 

 therefore, the probable validity of the assumptions might be said to be 

 verified. 



Unfortunately, some recent experimental data by Katz [1939] on the 

 stimulation of nerve with alternating currents do not satisfy the general 

 equations. 



A survey of the theories so oddly at variance, yet with so much in 

 common, has failed to develop the fundamental laws governing the 

 phenomena of nerve conduction. Despite these limitations the simple 

 postulates set up as working hypotheses by Blair and extended by 

 Rashevsky [1933] embody a very good representation of the methods of 

 attack and are an excellent approximation representative of the experi- 

 mental data. 



Blair postulated the existence of a local excitatory process (p) and a 

 stimulus (S). The growth of p in time, due to the stimulus, may be pro- 

 portional to the applied stimulus (S), to the applied energy (*S 2 ), or to 

 both. In mathematical terms these assumptions are 



^ = KS or f = KS> or * = &&) 



dt dt dt " ' ' 



Let us examine each one of these assumptions in terms of the known data. 

 It was found that, when a nerve fiber was made part of a closed electric 

 circuit and a stimulus in the form of a direct current was suddenly 

 applied, the excitability of the nerve was increased at the cathode con- 

 tact proportional to the intensity of the current strength. This fact 

 makes the second and third postulates untenable. We therefore retain 

 the assumption that the time rate at which the excitatory process (p) is 

 built up is proportional to the applied stimulus. 



dt 



where K is the constant of proportionality, i.e., the growth per second 

 per unit stimulus. 



* Blair perfected his analysis and supported it by experimental evidence in 1933 

 and 1934. 



