432 BUREAU OF ANIMAL INDUSTRY. 



iujudicious use of cold water when the system is heated, to a fault in 

 drainage, ventilation, or lighting of the stables, to indigestion, to liver 

 disease, to urinar}^ disorder, etc. 



STKUCTURE OF THE SKIN. 



The skin consists primarily of two parts: (1) The superficial non- 

 vascidar (without blood vessels) layer, the cuticle, or epidermis; and 

 (2) the deep vascular (with blood vessels) layer, the corium, dermis, 

 or true skin. 



The cuticle is made up of cells placed side b}' side and more or less 

 modified in shape by their mutual compression and by surface evapo- 

 ration and drying. The superficial stratum consists of the cells dried 

 in the form of scales, which fall off continuall}^ and form dandruff. 

 The deep stratum (the mucous layer) is formed of somewhat rounded 

 cells with large central nuclei, and in colored skin containing numer- 

 ous pigment granules. These cells have prolongations, or branches, b}^ 

 which they communicate with one another and with the superficial layer 

 of cells in the true skin beneath. Through these prolongations thc-y 

 receive nutrient liquids for their growth and increase, and pass on 

 liquids absorbed by the skin into the vessels of the true skin beneath. 

 The living matter in the cells exercises an equally selective power 

 on what the}^ .shall take up for their own nourishment and on what 

 they shall admit into the circulation from without. Thus, certain 

 agents, like iodine and belladonna, are readil}?^ admitted, whereas 

 others, like arsenic, are excluded by the sound, unbroken epidermis. 

 Between the deep and superficial layers of the epidermis there is a 

 thin translucent layer (septum lucidum) consisting of a double stratum 

 of cells, and forming a medium of transition from the deep spheroidal 

 to the superficial scaly cuticle. 



The true skhi, or dermis^ has a framework of interlacing bundles of 

 white and yellow fibers, large and coarse in the deeper layers, and 

 fine in the superficial, where they approach the cuticle. Between the 

 fibrous bundles are left interspaces which, like the bundles, become 

 finer as they approach the surface, and inclose cells, vessels, nerves, 

 glands, gland ducts, hairs, and in the deeper layers fat. 



The superficial layer of the dermis is formed into a series of minute 

 conical elevations, or papilla, projecting into the deep portion of the 

 cuticle, from which they are separated by a very fine transparent 

 membrane. This papillary layer is veiy richly supplied with capil- 

 lary blood vessels and nerves, and is at once the scat of acute sensa- 

 tion and the point from which the nutrient lic^uid is supplied to the 

 cells of the cuticle above. It is also at this point that the active 

 changes of inflammation arc especiall}^ concentrated; it is the immedi- 

 ately superposed cell layers (mucous) that become morbidly increased 

 in the early stages of inflammation; it is on the surface of the papillary 



