334 MATHEWS. 



There are two possible fallacies in Heidenhain's argument. 

 One fallacy probably lies in his tacit assumption that the gland 

 secretes as a whole ; that the secretion following a strong stimu- 

 lus is derived from the same alveoli as the secretion following a 

 weak stimulus. The other fallacy is the assumption that all of 

 the organic constituents of saliva secreted from a fresh gland 

 upon a strong stimulus are in solution. The true reason why 

 the dilator-secretory nerve may cause an increase in the organic 

 matter present in a secretion, coincident with an increased rate 

 of flow, in passing from a w^eak to a strong stimulus, may be 

 the following : 



If a very weak stimulus be used, only a portion of the alveoli 

 are aroused to activity. The supply of stored up products 

 (hylogens) in these, becomes soon exhausted and the secre- 

 tion derived from them is poor in organic constituents. On 

 passing to a strong stimulus, the previously resting alveoli are 

 thrown into activity and the secretion derived from them is rich 

 in organic constituents. It is the secretion from these fresh 

 alveoli, which increases the percentage of organic constituents 

 in the whole secretion. On passing from a long continued 

 weak to a strong stimulus in a fresh gland, one is really pass- 

 ing from an exhausted to a fresh portion of the gland. 



Moreover, in Heidenhain's observation there is a second 

 source of error which he has overlooked. Heidenhain treats all 

 of the organic constituents of the rapidly secreted saliva as if 

 they \vere in solution and considers that the liquid derived from 

 the blood is in contact with the materials to be dissolved, only 

 during the time of its passage through the cell. There can be 

 little question, how^ever, that saliva, and particularly the rapidly 

 secreted saliva of a fresh gland, cannot be considered a true 

 solution, for it contains many bodies in suspension. Heidenhain 

 himself has been one of those to describe the microscopical 

 appearance of the lumps of mucous matter, salivary corpuscles 

 and occasional leucocytes found in this secretion. The presence 

 of these bodies in saliva indicates that the rapidly secreted saliva 

 carries out of the cell not only substances in solution, but vis- 

 cous masses of mucous matter not in solution. Its swift cur- 



