g6 Spontaneous Secretion of Saliva 



removed from the body and perfused with blood from the carotid 

 artery via a system of tubing and cannulae or with plasma from a 

 motor-driven syringe. 



In all these instances the permanent flow could be due to agents 

 carried to the gland in the plasma. It might be suspected that such 

 an agent could originate in some part of the alimentarv canal. 

 Experiments on eviscerated animals showed, however, that the 

 sublingual gland continues to secrete for many hours at the same 

 rate as before the operation. This possibility of a blood-borne 

 secretory agent is ruled out in experiments in which a flow is 

 obtained even when Tyrode solution is used as perfusion fluid. 

 Furthermore, it is possible to dissect out the gland, with the duct 

 cannulated, and keep this thin structure alive in a bath of heated 

 and oxygenated Tyrode solution. Saliva of the characteristic vis- 

 cous type continues to flow from the cannula for about two hours 

 at about the same rate as in the natural surroundings and the 

 secretion can be accelerated by the addition of pilocarpine to the 

 bath (Fig. 5.1). The constancy of the rate of flow, and the simi- 

 larity with the rate seen in vivo, seems to rule out the possibility 

 that the isolated gland does not secrete but merely expels saliva 

 accumulated in the ducts before the gland was excised. 



The experiments described indicate that the sublingual gland of 

 the cat secretes spontaneously. This is not peculiar to the cat. In 

 the dog the denervated sublingual gland is in continuous secretory 

 activity (Emmelin, unpublished observation). Colin (1871) had, 

 in fact, been able to cannulate separately the sublingual duct of 

 the ox and observed a flow of saliva even between meals, a fact 

 which he found surprising, considering Claude Bernard's view 

 that the function of this gland is to facilitate swallowing by lubri- 

 cating the food. Very likely this secretion in the ox during periods 

 of digestive rest is at least partly a spontaneous process, although a 

 reflex activity has not been excluded experimentally. 



It is interesting that in the rabbit, which lacks the glandula 

 sublingualis major, the submaxillary gland is in a state of low 

 continuous secretory activity even after denervation or the injec- 

 tion of atropine or dihydroergotamine (Nordenfelt and Ohlin, 



1957). 



Probably the small salivary glands of the oral mucosa behave like 

 the sublingual gland. When saliva from the big glands is drained 

 off from the mouth, small amounts of thick saliva drain into the 



