336 PROTOPLASM 



irregular fluctuations in activation occur, until a level of complete 

 passivity is reached. All these reactions are duplicated in living 

 nerve tissue. Lillie points out that the dissimilarity in the 

 chemical constitution of iron wire and nerve fiber in no way 

 contradicts the identity of the fundamental physical reactions 

 in the two systems. 



The work of Ralph Lillie established a foundation for subse- 

 quent investigations. Other suggestions were made, such as 

 local movements of ions by diffusion, but this would be too slow 

 to account for the very rapid transmission of nerve stimuli. A 

 flow of electrons in the sense of a true electric current has also 

 been suggested. Emphasis on the chemical nature of nerve 

 transmission is based on the fact that a nerve slowly loses its 

 conductivity under conditions of asphyxia and recovers with 

 oxygen, which suggests a chemical reaction (oxidation reduction) 

 as the process responsible for the activity, but we have seen that 

 this is also the basis of Lillie's hypothesis (there is no essential 

 difference here between what is chemical and what is physical). 

 Physiologists are now generally agreed that the nerve stimulus 

 is an electric disturbance, wavelike in character. The velocity 

 of the waves has been established to be between 30 and 90 m. per 

 second, and their length about 18 mm. Erlanger, Bishop, and 

 Gasser have photographed the wave. 



Two other workers, E. D. Adrian and D. W. Bronk, have 

 carried studies of nerve transmission to a very refined point, 

 especially in regard to technique. Adrian supports the con- 

 clusions of Lillie, that the activity of neurons or nerve cells and 

 fibers is rhythmic owing to a rapid breakdown and repair of their 

 surface films. The larger nerve fibers or trunks are like cables 

 in that they are bundles of many finer fibers each of which is 

 capable of carrying an independent message. There may be a 

 thousand such fibers in one fair-sized nerve. It has been the 

 contribution of Bronk that a single fiber can be dissected apart 

 from the others and left intact, and its message alone studied and 

 recorded (Fig. 150). The extraordinary conclusion is reached 

 that the kinds of nerve impulses (whether sight, hearing, touch) 

 are alike in magnitude, rate of travel, etc. The frequency of 

 the nerve impulses depends on the intensity of the stimulus; 

 they vary from 300 to as low as 10 per second. How, then, is one 

 kind of message distinguished from another? This is done by 



