40 SECRETION 



even if the cervical cord is sectioned. Sweat centres are, there- 

 fore, surmised in the cord as well as in the medulla, but they 

 have not been definitely demonstrated. 



Sebaceous Secretion. This is an oily, semiliquid material, 

 which sets on exposure to air, and consists of water, salts, albumin, 

 cholesterin, fats, and fatty acids. Its function is to keep the 

 hair oiled, and perhaps to prevent too great a loss of water 

 through the skin, and also too great an absorption. The 

 sebaceous glands are usually found in connection with hairs 

 all over the body, but on the prepuce, ' glans penis, and lips 

 they occur separately. The secretion of the prepuce is known 

 as smegma preputii; that of the external auditory canal as 

 cerumen; that of the skin of the newly born as vernix caseosa. 

 In the formation of the secretion the gland cells break down 

 bodily and are replaced by new cells from the layer nearest 

 the basement membrane. 



Mammary Glands. The secretion of the mammary glands 

 is an alkaline, bluish-white fluid, having a specific gravity of 

 1030. It is a typical emulsion, consisting of a fluid plasma 

 holding suspended fat globules. When the secretion takes 

 place from a newly active gland there are, besides the fat 

 globules, certain albuminous bodies known as colostrum cor- 

 puscles, which may be cells of the gland or may, perhaps, 

 have their origin in wandering connective-tissue corpuscles. 

 The plasma of the milk consists of water holding in solution 

 casein, lactoalbumin, lactoglobulin, lactose, salts, traces of 

 urea, creatin, and creatinin. The fat globules consist chiefly 

 of stearin, palmitin, and olein, which upon standing rise to 

 the surface as cream. Their number in 1 c.c. of milk has been 

 estimated to be from 1,000,000 to 6,000,000. They are not, as 

 was formerly believed, surrounded by an albuminous envelope. 

 Through their high refractive power they are chiefly responsible 

 for the color of milk. The casein which is held in solution by 

 calcium phosphate is, however, partly the cause of the color 

 of milk. 



The reaction of milk is often amphoteric, and may, especially 

 in carnivora, be acid. Fresh milk is not coagulated by heat, 

 but upon standing it slowly becomes acid through the forma- 

 tion of lactic acid by fermentation, and will then curdle if 

 heated. The scum forming on cooked milk is a combination 



