LACHRYMAL GLAND THE TESTIS. 657 



this is composed are Albumen, Mucus, and a peculiar substance termed Ptya- 

 lin, which is soluble in water, insoluble in alcohol, and yet is different either 

 from albumen or gelatin. A considerable proportion of saline and earthy 

 matter exists in the solid residue of saliva ; this is nearly of the same cha- 

 racter as that which the blood contains, being chiefly composed of the phos- 

 phate of lime and soda, the chlorides of sodium and potassium, and the lac- 

 tates of soda and potash. One remarkable property of the salivary secretion, 

 is its formation of a rust-red precipitate when mixed with a solution of per- 

 salt of iron. This is supposed to be due to the presence in it of the prin- 

 ciple termed sulpho-cyanogen. The tartar which collects on the human teeth 

 consists principally of the earthy phosphates, the particles of which are held 

 together by about 20 per cent, of animal matter ; and nearly the same may 

 be said of the salivary concretions which occasionally obstruct the ducts. It 

 appears from various recent experiments, that the peculiar animal matter of 

 the Saliva has a decided effect in metamorphosing certain alimentary sub- 

 stances, and thus performs the first part of the digestive process. Starch may 

 be converted into sugar, and sugar into lactic acid, by its agency ; and if acidu- 

 lated, it has a solvent power for caseine, animal flesh, and other albuminous 

 substances ( 669). 



864. The Pancreatic Secretion of Man cannot, of course, be readily ob- 

 tained for analysis ; that which is procured from the lower animals, however, 

 probably gives a sufficiently correct idea of its character. It seems to be of 

 a nearly similar nature with saliva, but usually contains a much larger propor- 

 tion of solid matter; in that of the Dog as much as 87 parts in 1000 have 

 been found ; and in that of the Sheep, 40 parts. The probable offices of this 

 secretion in the digestive process, have been already noticed ( 669, 670). 



6. Lachrymal Gland. 



865. The Lachrymal glands and their secretion may be next mentioned ; 

 but neither require any lengthened description. The gland in Man is formed 

 very much on the plan of the Parotid, being composed of branched canals 

 terminating in follicles, the ultimate ramifications of the several branches 

 forming lobules or divisions of the glands. The lachrymal fluid has not re- 

 cently undergone any accurate analysis ; and all that can be stated respecting 

 it is the general fact, that the quantity of solid matter in it is extremely small, 

 and that this consists chiefly of saline, and either mucous or albuminous 

 compounds. It seems probable that the secretion of the lachrymal gland 

 itself is very little else than the serum of the blood, deprived of a great part 

 of its albumen ; and that the mucus of the tears is secreted from the surface 

 of the conjunctival membrane. This secretion has a slightly alkaline reac- 

 tion. It is being constantly formed in moderate amount, for the purpose of 

 cleansing the surface of the eye from the impurities which would otherwise 

 rest upon it ^ and it is then absorbed by the open orifices of the nasal duct, 

 and carried into the nose, as fast as it is poured out. The cause of this ab- 

 sorption does not seem very clear. Capillary attraction is probably in part 

 concerned; and it has been thought that the momentary partial vacuum, oc- 

 casioned by the inspiratory effort in all the air-passages, will cause the empty- 

 ing of the nasal duct below, and a consequent in-draught above. The influ- 

 ence of the nervous system upon this secretion has been already adverted to 

 ( 625, 626). 



7. The Teslis. Spermatic Fluid. 



866. In the Testes we return to the tubular form of glandular structure, 

 which so remarkably distinguishes the Kidney from all the other glands 



