GLANDULAR SECRETIONS. 87 



The salivary secretion is not necessarily constant, it takes place 

 during the movements of mastication, and when any irritant is taken 

 into the mouth. It is alkaline in its reaction, and contains among 

 other ingredients, a peculiar animal principle, analogous to pepsine, 

 called ptyaline, which seems to act as a ferment, since by it starch 

 may be converted into sugar, and sugar into lactic acid. A consider- 

 able proportion of saline and earthy matter exists in the solid residue 

 of the saliva; this is nearly the same as that the blood contains. 

 The tartar of the teeth consists principally of one of these, the earthy 

 phosphates, held together by a little animal matter. If the alkalinity 

 of the saliva be destroyed, it loses its converting power on starch ; 

 and if acidulated, it has a solvent power for caseine, animal flesh, 

 and other albuminous substances. The specific gravity varies from 

 1-006 to 1*009. The qumitity secreted during 24 hours has been 

 estimated at about 15 or 20 ounces. 1^\\q, pancreatic secretion con- 

 tains a larger proportion of solid matter than the saliva. 



The Maiumary Secretion is peculiar to the niatnmalia, and is one 

 of those which are destined for special uses in the economy. The 

 gland is found in both sexes, and presents but little difference in 

 them till the period of puberty. It consists of numerous lobules held 

 together by areolar tissue. Each lobule consists of a series of ducts 

 passing inwards from their termination in the nipple, and then rami- 

 fying like the roots of a tree, their ultimate subdivisions terminating 

 in minute follicles. The mammillary tubes are ten or twelve in num- 

 ber ; they are straight ducts terminating in the nipple, and having a 

 slight dilatation just before their termination, which acts as a reservoir 

 to receive the secreted milk. The secretion, as in the other glands, 

 takes place in the ultimate follicles, by means of cells, which dis- 

 charge themselves into the ducts. (Fig. 20.) 



The mammary gland of the male is a minia- 

 ture of that of the female, but it does not undergo Fig. 20.* 

 any marked increase in size at any particular 

 period, its evolution going on pari passu with 

 that of the body. There are some instances on 

 record (one by Dr. Dunglison,) of its secreting 

 milk; in Dr. Dunglison's case, the secretion 

 was induced by the individual applying the 

 children entrusted to his care, to the breasts 

 during the night. 



The milk consists of water holding in solution 

 sugar, various saline ingredients, and a peculiar 

 albuminous substance called caseine^ and having 

 oleaginous particles suspended in it. By allow- 

 ing the milk to stand, the oil-globules will come 



* A vertical section of the Mammary Gland, siiowing its thickness and the origins of the 

 lactiferous ducts ; 1, 2, 3, its pectoral surface ; 4, section of the skin on the surface of the 

 gland ; 5, the thin skin covering the nipple ; 6, the lobules and lobes composing the gland ; 

 7, the lactiferous tubes coming from the lobules ; 8, the same tubes collected in the nipple. 



