274 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



varies from 19.3' to 22.5 c.c, while from 22.9 to 42.5 c.c. of CO, are 



liberated on the addition of phosphoric acid. 



The secretions of the different glands of the salivary system present 



several distinguishing points which will be alluded to in turn. 



1. The Parotid Secretion. — 

 In order to study the pure secre- 

 tion of the parotid gland, the 

 saliva must be collected before 

 it reaches the mouth to be mixed 

 with fluid from the other glands. 

 This may be accomplished, in 

 man or in the dog, by catheter- 

 izing the parotid duct, an oper- 

 ation which is readily performed. 

 It is only necessary to open the 

 mouth and evert the cheek, when 

 the papilla of entrance may be 

 recognized on the inner surface 

 of the cheek, on a level with the 

 second molar tooth of the upper 

 jaw. A slender glass tube or 



silver cannula may be readily inserted within the orifice of the duct and 



the fluid collected as it flows through the tube. Where studies as to the 



Fig. 111.— Parotid and Submaxillary Glands 

 of the Dog, with their Excretory 

 Ducts. (Biclard.) 



p, parotid gland : m, submaxillary gland ; a, duct of Steno ; 

 r, duct of Wharton ; v, maaseter muscle ; I, temporal muscle. 



Fig. 112.— Relations of the Parotid Duct, of the Dog with the 



Facial Vessels and Nerve, after Bernard. 



The dotted line indicates the line of incision for finding the duct at the apex of the angle formed by 



the vessels and nerve. V. vasculo-nervous fasciculus forming the inferior side of the angle ; N, fasciculus 



forming the upper side ; D, point of junction of these two fasciouli ; C, duct of Steno biseotiug'this angle. 



mechanism of secretion have to be made, or where a considerable quan- 

 tity is to be- collected, a more convenient method is to make a fistulous 



