326 DISEASES OF CATTLE. 



ous extremity, is lighter aud softer than the stern, and lodged in a 

 recess or hair follicle, which may either be in the corium or subcuta- 

 neous areola?. The follicle is dilated at the bottom to correspond with 

 the root-bulb, and the ducts of one-or more sebaceous glands open into 

 it. At the bottom of each follicle is a conical vascular papilla, similar 

 in every respect to those on the surface of the skin ; this papilla fits 

 into a corresponding depression in the root of the hair. The shaft con- 

 sists of a center or medulla, a surrounding fibrous portion, and an 

 external coating or cortex. The medulla consists of cells containing 

 pigment or fat, is opaque, and deeply colored. All hair has not this 

 medulla. The fibrous portion occupies the bulk of the stem, and the 

 cortex is merely a single layer of thin, flat, imbricated scales. 



The sebaceous glands, lodged in the corium, are most abundant in 

 parts exposed to friction. They generally open into the hair follicles, 

 occasionally on the surface of the body. Each gland consists of a 

 small duct, which terminates in a lobulated recess. These lobules 

 vary, and are, as is the duct, lined with epithelium. They are filled 

 with sebaceous matter, which, as it is secreted, is detached into the 

 sacs. They are very plentiful between the claws of cattle. 



The sudorific glands, or sweat glands, are situated in the subcuta- 

 neous areolar tissue, surrounded by a quantity of fat. They are small, 

 round, reddish bodies, each of which consists of one or more fine tubes 

 coiled into a ball, the free end of the tube being continued up through 

 the true skin and cuticle, and opening on the surface. Each sweat- 

 gland is supplied with a cluster of capillary blood-vessels which vary 

 in size, being very large when perspiration is excessive. The contents 

 of the smaller ones are fluid, and the larger semifluid. 



The skin may be regarded as an organ supplementary in its action 

 to the lungs and kidneys, since the skin by its secretion is capable 

 of removing a considerable quantity of water from the blood, small 

 amounts of carbon dioxide, and small amounts of salts, aud in cer- 

 tain instances during suppression of the renal secretions a small 

 amount of urea. The skin is also the chief organ for the regulation 

 of animal heat, by or through conduction, radiation, and evapora- 

 tion of water, permitting of loss of heat, while it also, through other 

 mechanisms, is able to regulate the amount of heat lost. The hair 

 furnishes protection against extreme and sudden variations of tem- 

 perature by the fact that liairs are poor conductors of heat, and 

 inclose between them a still layer of air, itself a nonconductor of 

 heat. The hairs are also furnished with an apparatus by which 

 the loss of heat may be regulated; thus, in cold weather, through 

 the contraction of unstriped muscular fibers of the skin, the hairs 

 become erect and the external coat becomes thicker. Cold, too, 

 acts as a stimulus to the growth of hair, and we find in consequence a 

 thicker coat in winter than in summer. The hairs also furnish protec- 

 tion against wet, as they are always more or less oily from the secretion 



