312 A MANUAL OF VETERINARY PHYSIOLOGY 



supports the prejudice which has always existed against this 

 practice. It is evident that with free grooming the loss in fat 

 alone is something considerable, and the animal exposed to 

 chill. The amount of fat depends upon the nature of the diet ; 

 on a purely hay diet there is very little fat in the dandruff, while 

 on oats there is a considerable amount. The urea shown in the 

 analysis is no doubt derived from the sweat. 



Dandruff contains a colouring matter found by the writer to 

 be chlorophyll which has undergone modification by passing 

 from the digestive canal to the skin. The use of this pigment is 

 unknown ; in fact, the horse is the only vertebrate in which 

 chlorophyll has so far been found as a constituent of any cuta- 

 neous excretion. 



In certain places, as in the prepuce, considerable quantities 

 of sebum are found. The sebaceous secretion of the prepuce 

 of the horse consists of 50 per cent, fat, and also contains calcium 

 oxalate. The ear-wax and eyelid secretions are also of a 

 sebaceous nature. In the sheep a considerable quantity of fatty 

 substance is found in the wool ; it exists in two forms, (1) as a 

 fatty acid united to potash to form a soap, and (2) a fatty acid 

 combined with cholesterin instead of glycerin ; the latter is 

 known as lanolin, and is largely used as a basis for ointments. 

 It is also found in hair, horn, feathers, etc. The fatty substance 

 in the wool is known to shepherds and others as ' suint.' In 

 merino sheep it may amount to more than one-half the weight 

 of the unwashed fleece, but in ordinary weather-exposed sheep 

 it may be 15 per cent, or less. The large amount of potash in 

 unwashed wool is very remarkable ; a fleece sometimes contains 

 more potash than the whole body of the shorn sheep (Warring- 

 ton). 



Respiratory Function of the Skin. — Certain vertebrates such 

 as the frog can respire by the skin in the entire absence of lungs ; 

 in this way they absorb oxygen and excrete carbonic acid. 

 Observations made on animals and men have demonstrated that 

 similar changes occur through the skin, but on a very small 

 scale. 



Varnishing the skin rapidly causes death in rabbits, and more 

 slowly in horses. Death is due to loss of body-heat, and not 

 to the retention of poisonous products, as was at one time sup- 

 posed. Bouley* states that horses shiver when varnished, and 

 the surface of the body and the expired air become colder, the 

 visible membranes respond by becoming violet in tint, and the 

 animals die after several days. According to Ellenberger, if 

 only partly varnished they do not die, but exhibit temporary 



* Colin's ' Physiologic Comparee.' 



