68 AMERICAN FARMER'S HORSE BOOK. 



THE SALIVARY GLANDS — SECRETION AND EXCRETION DEFINED. 



"A gland may be defined to be an organ whose office it is 

 to separate from the blood some peculiar substance, which is 

 poured out through an excretory duct, whose internal surface 

 is continuous with the mucous membrane or skin. 



"By secretion is understood the process of separation of 

 various matters from the blood, the term being also applied 

 to the products of the process, such as saliva, bile, etc., which 

 are commonly known as secretions. These are all removed 

 from the blood for one of two purposes ; first, in order to be 

 employed for some ulterior object in the various processes 

 going on in the body, either for its own preservation or that 

 of others ; or, secondly, as being injurious to its welfare, and, 

 therefore, to be discarded." 



It has been customary to distinguish this function accord- 

 ing as it has for its object one or the other of the purposes 

 above indicated. By this distinction, the term secretion is 

 limited to the former action, while the latter receives the 

 name of excretion. These are the senses in which the terms 

 are used in this work. 



The throat is a part of the horse's frame that is plentifully 

 supplied with glands. It has three sets of these, throwing 

 out their secretions of saliva to form the spittle of the mouth. 

 In the horse, although there is somewhat less of this dis- 

 charge than in the human being, its quantity is surprisingly 

 great, not less than four or five gallons in every twenty-four 

 hours. The principal use of the saliva is to moisten the food 

 during the proQCSs of mastication. 



The most important of the salivary glands is the parotid. 

 This is placed in the hollow that extends from the root of 

 the ear to the angle of the lower jaw-bone. It is composed 

 of numerous small glands, uniting in one common duct, that 

 discharges its contents into the mouth opposite the second 

 jaw tooth. The quantity of fluid secreted by the parotid 

 gland alone is estimated to be not less than one pint per 

 hour, and, during mastication, nearly twice as much. It is 



