NERVOUS SYSTEMS, PERIPHERAL AND CENTRAL 471 



thinks that the conceptions of neuro-fibrils and Nissl substance are apt to lead 

 astray in the interpretation of phenomena taking place during life. His 

 observations were made on ganglion cells mounted in serum or cerebrospinal fluid 

 of the animal whose cells were under observation, and they were kept at body 

 temperature. The granules are extremely minute, not more than 1 p. in diameter, 

 and they appear themselves to consist of a colloidal solution surrounded by a 

 lipoid envelope. This envelope stains deeply with methylene blue. 



The observations of Ross Harrison on the outgrowth of nerve fibres have 

 already been mentioned (page 22). They suggest strongly an amoeboid movement 

 of the processes of the nerve cell, at all events in the embryonic state, and show 

 that the nerve fibres grow out from cells in the central nervous mass, thus 

 placing the neurone doctrine beyond question (see Fig. 20). If this amoeboid 

 nature of the branches of the cells continues in the adult, the possibility is present 

 of influence by changes of surface tension, due to excitation processes in the cell, 

 and an effect on the degree of contact with other neurones. 



Contrary to the nerve fibre itself, the cell body of the neurone is very sensitive 

 to deprivation of oxygen, both cytoplasm and nucleus becoming swollen. Similar 

 changes occur when the axone is injured, and the power of recovery depends 

 on the degree of the injury. If recovery takes place, the axone grows out again 

 to the periphery. 



From the effect of raised temperature, Mott concludes that there are at least 

 two colloidal substances in the living cell, fluid granules with delicate membranes 

 and a viscid homogeneous semi-fluid substance forming the external phase. The 

 membranes on the surface of the internal phase are, doubtless, produced by 

 adsorption. Rise of temperature causes the granules to blend with the external 

 phase. 



The fact that each lateral half of the electrical organ of Malapterurus is 

 innervated by one single large efferent neurone enabled Gotch and Burch (1896) 

 to investigate certain elementary properties of the mode of discharge of the nerve 

 cell. Although caution must be exercised in extending these results to all efferent 

 neurones, they give valuable indications of the phenomena possible. The response 

 to a peripheral stimulus is usually multiple, that is, a rhythmical series of discharges. 

 In fatigue, the number of discharges per second is decreased before the intensity of 

 each individual discharge falls. The time taken by an impulse to pass from the 

 afferent to the efferent side of a cell is from O008 to O'Ol second and is increased 

 by fatigue. 



It is somewhat difficult to state what is actually the function of the cell body of 

 the neurone, apart from being the meeting place of fibres from various other neurones 

 and thus allowing for the connection of a number of afferent arcs with the same 

 " final common path." It seems that it must act in reinforcing impulses which 

 might be too weak to set up a disturbance in a fresh neurone. The refractory 

 period, no doubt, plays a part and we must also suppose that changes in the cell 

 body are able to prevent the reception of impulses coining from sources extraneous 

 to those connected with the particular act in which the neurone is engaged at a 

 given moment. In certain cases it seems that it is not necessary that the impulses 

 should pass through the actual cell body itself. When this lies, as it were, on a 

 side branch of the nerve fibre, the continuation of this fibre may branch and act as 

 dendrites to form connection with another neurone. This fact has only been 

 clearly shown for one case, namely, that of the crab, in which the cell bodies lie on 

 the surface of the ganglion mass, and Bethe (1897 and 1898) has succeeded in 

 cutting them off, leaving the reflex to be conveyed through the neuropile. After a 

 time the reflex disappears, presumably because the trophic action of the cell body 

 with its nucleus has gone. 



A less convincing experiment of the same kind was made by Steinach (1899) on the dorsal 

 root ganglia of the frog. By separating these ganglia from their blood supply, it was found 

 that the cells degenerated after about fourteen days, but that the sensory impulses were still 

 transmitted through the ganglia. If these results apply to neurones in general, it must be 

 admitted that the actual cell substance itself has very little function, except that of nutrition, 

 and the main physiological activities must be relegated to the synapses. 



The cell bodies have the usual needs of cells undergoing metabolic changes, 



