GENERAL CONSIDERATIONS. 527 



a growth of protoplasm is derived from the microscopical examination 

 of the various glands, after stimulating the sympathetic. Thus, 

 according to Heidenhaiii to take the most striking example adduced 

 by him if the cervical sympathetic be stimulated in the dog for several 

 hours, there is no secretion from the parotid gland, but the gland-cells 

 show a great increase in carmine-staining material, i.e. a considerable 

 growth of protoplasm. 



I have not been able to convince myself that any considerable 

 changes of this nature take place. On stimulating the sympathetic the 

 thick secretion usually stops up the ducts, and if any further secretion 

 takes place it can only pass out into the lymph spaces. After 

 stimulating the sympathetic for five to seven hours, I do not find any 

 marked increase in the staining power of the cells ; and the fresh gland 

 either shows no outer non-granular zone at all, or a very small one. 



The evidence that a separate class of trophic nerve-fibres exists, 

 which converts stored-up material into a more soluble form, rests on 

 certain facts, which we will discuss as far as possible separately. In the 

 first place, there are the facts adduced to prove that soluble substance is 

 formed during secretion, and which do not touch the question whether 

 the formation is due to a special nerve-fibre or not. 



1. It was shown by Heidenhain that the percentage of organic 

 substance in saliva, secreted under the influence of the cranial nerve, 

 increases with the rate of secretion. On this fact Heidenhain argued 

 somewhat as follows : If the solvent power of the fluid passing through 

 the cells remains constant, and the solubility of the stored-up substance 

 in the cell also remains constant, the amount of the stored-up substance 

 dissolved by the fluid in its passage through the cell will decrease as the 

 rate of its passage increases. For, below saturation point, the amount 

 dissolved must decrease the less the time the solvent is in contact with 

 the solvend. But, in fact, the slower the passage of the solvent the less 

 it dissolves ; hence, with increasing rate of flow, there must be either an 

 increase in the solvent power of the fluid, or an increase in the solubility 

 of the stored-up substance. Heidenhain considered that in mucous 

 saliva, at any rate, the only substance which could increase the solvent 

 power of the fluid was sodium carbonate. And this salt, he found, did 

 not increase, as saliva was secreted more rapidly. In consequence, 

 he concluded that the substance in the cell must become more soluble. 

 An increase in solubility of part of the stored-up substance was then a 

 result of stimulating nerve-fibres. 



But it is by no means clear that the rapidly-secreted fluid is not a 

 better solvent than the fluid secreted slowly. Werther, working in 

 Heidenhain's laboratory, found in fact that the percentage of sodium 

 carbonate in the submaxillary saliva of the dog does increase, though 

 but slightly, with the rate of secretion of saliva. And, in addition, it 

 cannot be regarded as certain that sodium chloride and other neutral 

 salts do not aid in the solution of the substances stored up in the cells. 

 The evidence, indeed, seems to me to be on the other side. And, as we 

 have seen, when saliva is secreted more rapidly, there is an increase in 

 the percentage of salts as well as in that of organic substances. Finally, 

 the statement that the faster the fluid passes through the cell, the less 

 substance it will dissolve, depends on the assumption that in slowly- 

 secreted and in rapidly-secreted saliva, the fluid has an equal oppor- 

 tunity of dissolving the stored-up material. This is not necessarily the 



