THE SALIVA. 121 



exceed 1500 c.c. It depends upon the amount of nutriment in- 

 gested, the act of chewing, the character of the food, the mental 

 condition, etc. Fright may arrest its flow entirely. After the 

 administration of pilocarpin or during the inhalation of ether an 

 abundant secretion of saliva occurs. Atropin acts in the opposite 

 manner, and can arrest the flow entirely. 



To a certain extent the amount secreted is dependent upon the 

 blood-pressure, but it does not follow that the saliva results from the 

 blood-plasma through a simple process of filtration. We find that 

 in the submaxillary gland, for example, the secretion continues for 

 some time even after decapitation of the animal. The secretory 

 pressure, moreover, is very much greater than the blood-press- 

 ure ; and after the administration of atropin, which paralyzes the 

 secretory nerves, we further find that while electrical stimulation 

 of the chorda calls forth an increased circulation in the gland, a 

 secretion of saliva does not occur. These experiments show that 

 the secretion of the saliva cannot be referable to a simple process 

 of filtration, but must depend upon a special secretory activity on 

 the part of the alveolar cells. We thus also find that the salivary 

 glands are capable of eliminating certain chemical substances, such 

 as bromides and iodides, from the body, while others, like iron com- 

 pounds, for example, are not removed through this channel, if we 

 disregard the trace which is normally present. 



Chemical Composition. The chemical composition of the saliva 

 is qualitatively fairly constant. Quantitative variations, however, 

 are common. This is to a certain extent owing to the fact that the 

 different glands are not all of one kind. In the human being the 

 parotids are thus albuminous glands, the sublinguals mucous glands, 

 while the submaxillary glands furnish a mixed secretion. The 

 character of the secretion, moreover, may vary with one and the 

 same gland. The salivary glands all have a double nerve-supply, 

 which is partly of cerebral origin and partly derived from the sym- 

 pathetic system, and as the one or the other set of fibres exercises 

 its stimulating effect, the composition of the individual secretions 

 will vary. In the submaxillary gland of the dog, in which these 

 relations have been especially studied, on stimulation of the sym- 

 pathetic fibres a secretion is furnished which is less abundant, but 

 contains a larger amount of solids, than the secretion obtained on 

 stimulation of the chorda. This is well shown in the following 

 table, which is taken from Kiihne : 



Sympathetic saliva. Chorda saliva. 



Specific gravity . . . 1.007-1.018 1.004-1.006 



Solids 16-18 pro mille 12-14 pro mille 



On dividing all the nerves which supply the salivary glands, or 

 following the administration of curare, the secretion still continues 

 for a while, but the saliva which is thus furnished contains scarcely 

 any solid material, and is termed paralytic saliva. 



