THE SALIVA. 523 



or facial, but from the auriculo-ternporal branch of the fifth pair. As 

 already stated (p. 264), irritation of the sympathetic branches supplying 

 the sublingual and submaxillary glands, has an opposite effect to that 

 of stimulating the fibres of the chorda tympani; the secretion from 

 the glands then becomes scanty and thick, the arteries small, the flow 

 of blood through the gland diminished and retarded, and the venous 

 blood dark. To explain these opposite phenomena, it is assumed that 

 the sympathetic nervous centres cause a contraction of the muscular 

 coats of the smaller arteries ; whilst the cerebro-spinal centres inhibit 

 this power, and so induce a relaxed condition of the arterial coats. 

 The efferent effect, conveyed through the chorda tympani nerve-fibres, 

 is therefore not motor, but of a special kind, controlling, or inhibiting 

 the action of the sympathetic nerve-fibres and centres. This example 

 will suffice to illustrate the mode in which secretion generally is be- 

 lieved to be influenced through the nervous system. Irritation of the 

 sympathetic nerves does not alter the quality, but only lessens the 

 quantity, of the secretion of the parotid glands. According to Eck- 

 hard, great numbers of mucous corpuscles, exhibiting intrinsic move- 

 ments, like those of the Amoeba, are found in the viscid secretion of 

 the sublingual and submaxillary glands, after irritation of their sympa- 

 thetic nerves; such corpuscles, but in smaller number, exist, as we 

 shall see, in ordinary saliva. 



The chemical composition of the saliva is, according to Dr. Wright, 

 as follows : 



Water, . 



Ptyalin, or Salivin, 



Fatty matter, 



Albumen with Soda, 



Mucus, . 



Ashes, . . . 



Loss, 



98.81 . = 98.81 



.18 

 .05 

 .17 

 .26 

 .41 

 .12 



Solids . = 1.19 



100. 100. 



The saliva, thus constituted, is a transparent watery fluid, destitute 

 of smell ; its specific gravity varies from 1002 to 1008. Besides fine 

 granular particles, mucous corpuscles, derived, for the most part, from 

 the lingual and tonsillar glands, and epithelial cells detached from the 

 mouth, the saliva contains the so-called salivary corpuscles, spheroidal 

 nucleated cells, somewhat resembling the white blood-corpuscles, which 

 undergo Amoeba-like changes in form, and exhibit a molecular move- 

 ment in their interior. 



The quantity of saliva secreted in twenty-four hours by all the 

 glands, has been estimated at from 1 to 3 Ibs. ; but it differs according 

 to the nature of the food, and the intervals between the meals. Its 

 flow is increased by mastication, but is arrested by the cessation of 

 that movement. The saliva from the parotid gland is very thin and 

 watery, and becomes more abundant during mastication ; that from 

 the submaxillary, and especially from the sublingual gland, is more 

 viscid, and flows more constantly, for purposes of speech. The paro- 

 tid glands, when active, are said to secrete from eight to ten times 



