CHANGES CONSEQUENT ON FUNCTIONAL ACTIVITY. 455 



have estimated the capacity of the duct from the canula to the 

 gland, and am of opinion that it will contain about three drops. 

 The quantity is certainly very much smaller than the total 

 secretion which, in the period before the renewed excitation, 

 stagnated in the very numerous and, in some instances, very 

 wide ducts. Thus it appears that the originally clear saliva 

 contained in the duct has become cloudy, and obviously in 

 consequence of a pathological process ; for, if a freshly exposed 

 duct be emptied of its contents, even if the dog have previously 

 discharged no saliva, the secretion obtained on section is clear. 



The saliva caused to flow by irritation of the sympathetic 

 nerve contains a large number of spheroidal particles of mu- 

 cus, together with morphological elements of a less clearly 

 definable nature, but representing products of disintegration. 

 Heidenhain, however, was frequently unable to discover any 

 morphological elements. As this kind of saliva can only be 

 obtained in small quantity, the exudate that is poured forth 

 may perhaps never be completely washed out and evacuated, 

 and as only a small quantity of saliva appears at long inter- 

 vals, the fluid essentially consists of this. Heidenhain has 

 shown that when the excitation is long maintained it becomes 

 clearer. The relations of the sympathetic nerve to the salivary 

 glands are, however, involved in much obscurity. 



From what has now been adduced, it will be seen that fur- 

 ther observations are required before it can be admitted that 

 the saliva naturally contains formed elements. 



7. OF THE ALTERATION OF STRUCTURE IN THE GLANDS 



CAUSED BY THE PERFORMANCE OF THEIR FUNCTIONS. When 



the salivary glands have been long in action, they become 

 lighter, softer, paler in appearance, and both absolutely and 

 relatively poorer in solid constituents. After being long at 

 rest the inverse changes occur, and they assume a yellower 

 colour. This last I believe to be occasioned by the accumulation 

 of numerous molecules in the salivary cells. The gland becomes 

 "charged." Heidenhain has recently expressed the opinion, 

 that in some animals (Carnivora and Herbivora) the secretion is 

 accompanied by the disintegration of a certain proportion of 

 salivary cells, the place of which is supplied by a new genera- 



