306 A MANUAL OF VETERINARY PHYSIOLOGY 



affect the whole surface of the body, as in white (cream-coloured) 

 horses with a pink skin ; or large areas of the bodies of such 

 horses may be bay or black, and the remainder cream-coloured. 

 In cream-coloured horses the choroid and iris are without 

 pigment, the latter being bluish. A ' grey ' horse is not a • white ' 

 horse. 



Clipping. — Experience shows that the heavy winter coat grown 

 by horses is the cause of considerable sweating at work, and 

 the general practice of clipping has hence been introduced. Of 

 its value there can be no doubt ; it considerably reduces the risk 

 of cold and chest diseases, for animals on coming in from work 

 may be readily dried and thus protected from chills. Horses 

 which sweat freely at work soon lose * condition ' ; the writer's 

 observations have shown that this is due to the protein lost by 

 the skin, for, as we shall presently see, proteins are found regu- 

 larly in the sweat of the horse. Clipping largely prevents this 

 loss, though for this purpose it is not necessary to clip a horse 

 all over ; a half-clipped body suffices. The influence of clipping 

 on temperature is dealt with in the chapter devoted to Animal 

 Heat. 



Erection of Hairs. — In some animals, as, for instance, the dog 

 and cat, the hairs are rendered erect under excitement such as 

 anger or fear ; this is due to the involuntary muscle attached to 

 the hair follicle, and the process is under the influence of the 

 sympathetic nervous system. The fibres for the body-hair 

 emerge from the spinal cord by the inferior roots, pass to the 

 grey ramus of the sympathetic chain, and run to the skin by 

 the dorsal cutaneous nerves ; the fibres for the head and neck 

 are in the cervical sympathetic. Under the influence of cold the 

 hairs on the horse's body may become erect, but there is no 

 indication of this under psychical excitement, as in the case of 

 the dog and cat. It is possible that the prescience of a coming 

 storm or change of weather exhibited by cattle may probably be 

 due to the highly hygroscopic properties of their hair. Hair is one 

 of the few organic substances which elongate instead of shorten 

 as they grow moist. The effect of movement of every hair on 

 the surface of the body may cause a mechanical stimulation of 

 the hair-follicle nerves, and so give rise to an uneasiness which 

 presages the coming change. 



Sweat. — By means of glands in the skin a fluid termed ' sweat,' 

 and a fatty material known as * sebum,' are secreted. Sweat, 

 or perspiration, is not found to occur over the general surface 

 of the body in any other hairy animal than the horse. There are 

 certain parts of the skin which sweat more readily than others ; 

 the base of the ears in the horse is the first place where sweating 

 begins, the neck, side of chest, and back follow, lastly the hind- 

 quarters. No sweating takes place on the legs ; the fluid found 



