260 The Physiological Role of Saliva 



the dogs did not drink more water than before in Montgomery's 

 experiments (19316). In view of the fact that some glands may 

 secrete spontaneously and therefore even after atropinization, it 

 would be interesting to repeat this experiment also under condi- 

 tions of increased demands on the salivary secretion, for instance, 

 in panting dogs. An attempt to evaluate the different theories put 

 forward to explain the regulation of the water balance is beyond 

 the scope of this chapter and the competence of its author. The 

 problem has been surveyed by Gregersen (1956), who also gives the 

 literature quoted in this section. 



A role just mentioned is that which saliva plays in thermo- 

 regulation in some species. The salivary glands provide the water 

 which evaporates from the oral mucosa, particularly that of the 

 tongue in the panting dog. When exposed to a warm atmosphere 

 a dog begins to pant and thin watery saliva flows. The secretion is 

 evoked reflexly from the dry mucosa ; if the mouth is kept closed 

 or the tongue moistened with water, the salivary flow decreases 

 (Gregersen, 193 1). It even seems possible to develop a conditioned 

 reflex with secretion, elicited for thermoregulatory purposes, acting 

 as the unconditioned stimulus. 



It could be assumed that the sympathetic system engaged in 

 thermoregulatory reactions by acting on the sweat glands and the 

 blood vessels of the skin would cause the salivary secretion during 

 panting. This, however, is not the case. Alexandrov (1939) found 

 that salivation elicited by increasing the body temperature in dogs 

 by means of tetrahydronaphthylamine was abolished by para- 

 sympathetic denervation. 



It has been mentioned earlier that secretion of saliva is reduced 

 during fever in dogs. There need not be any conflict between this 

 fact and the findings described above. Hypersalivation results from 

 the polypnoea of panting and the consequent dryness of the pro- 

 truding tongue. There is not necessarily any panting in fever; the 

 reduced salivary responses to various stimuli during fever may be 

 due to a certain degree of dehydration. 



The use of saliva for toilet purposes provides a further example 

 of a function of the salivary glands mostly confined to certain 

 species, for example, the cat. The dog's licking of its wounds, sup- 

 posed to promote healing, may also be mentioned here; Pavlov 

 connected this function with the experimental finding that electri- 

 cal stimulation of various afferent nerves in dogs causes a flow of 



