GENERAL CONSIDERATIONS. 527 
a growth of protoplasm is derived from the microscopical examination 
of the various glands, after stimulating the sympathetic. Thus, 
according to Heidenhain — to take the most striking example adduced 
by h im — if the cervical sympathetic he stimulated in the dog for several 
hours, there is no secretion from the parotid gland, hut the gland-cells 
shew a great increase in carmine-staining material, i.e. a considerable 
growth of protoplasm. 
1 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 clue 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 
