430 VETERINAEY PHYSIOLOGY 



glands can be stimulated by certain drugs e.g. pilocarpine. 

 The action of heat seems also to be chiefly peripheral, setting 

 up an unstable condition of the gland cells so that they 

 respond more readily to stimulation. 



4. Chemistry of Sweat. Sweat from the horse is a sherry- 

 coloured fluid, which, when pure, has a neutral or faintly 

 alkaline reaction. Its specific gravity is about 1020 in the 

 horse, and it contains about 5'5 per cent, of solids, of which 

 5 per cent, are inorganic and about 0'5 organic. Potassium 

 is the most abundant base. Chlorides are present in small 

 amounts. The chief organic substances present are proteins 

 some globulin and some albumin. Fat is also present, 

 probably derived from the sebaceous secretions, and it com- 

 bines with the potassium to form a soap. 



B. Sebaceous Secretion. The sebaceous glands are simple 

 racemose glands which open into the hair follicles, and their 

 function is to supply an oily material to lubricate the hairs. 

 This secretion is produced by the shedding and breaking 

 down of the cells formed in the follicles of the glands. Those 

 lining the basement membrane are in a condition of active 

 division, but the cells thrown off into the lumen of the follicle 

 disintegrate and become converted into a semi-solid oily mass, 

 which consists of free fatty acids and of neutral fats of 

 glycerine and of cholesterin. These cholesterin fats are the 

 lanolins, which differ from ordinary fats in being partly 

 soluble in water. Free cholesterin is also present in the 

 sebum. 



C. Milk Secretion 1. Physiology. Before pregnancy occurs 

 the mammary glands are largely composed of fibrous tissue, 

 with a large amount of fat, in which run the branching 

 tubules of the glands as small solid blocks of cells. 



As pregnancy advances these tubules grow outwards and 

 increase, and the cells begin to divide, some remaining attached 

 to the basement membrane, some coming to lie in the middle 

 of the tubules. These latter undergo a fatty change and break 

 down, and they are shed in the first milk which is secreted, 

 the colostrum. The cells left upon the basement membrane 

 elaborate the constituents of milk, and the presence of fat 

 globules in their protoplasm is very manifest. 



The milk, after being secreted, collects in the ducts of the 



