260 STUDIES IN ADVANCED PHYSIOLOGY. 



of the nerves going to the submaxillary gland will materi- 

 ally aid: 



1. The cerebro-spinal nerves. If the nerve coming 

 from the brain and going to the submaxillary gland be cut, 

 and the end of the nerve connected with the gland be stim- 

 ulated, a copious secretion of saliva immediately results. At 

 first the saliva is perfectly normal, but as the gland is being 

 stimulated longer and longer, the secretion becomes more 

 and more watery, and finally contains little else than water 

 and dissolved salts. The ptyalin, the specific element of 

 saliva and the mucin are no longer present. If the nerve 

 or gland be not too much affected by excessive work such a 

 secretion of watery saliva may be continued for a long 

 time. 



From this experiment it is evident that the nerve from 

 the brain, the corda tympani, as it is usually called, causes 

 an abundant flow of a watery secretion from the gland, but 

 does not seem to be directly concerned in the production of 

 any of the specific elements of the secretion. What the 

 gland pours out is simply material which it has taken from 

 the blood. It is not anything which the gland has made 

 itself. Such parts of a secretion which are derived directly 

 from the blood are called transudations, and it seems that 

 the cerebro-spinal nerve is therefore directly concerned 

 with the transudations. These transudations, however, 

 serve to wash the specific elements out of the gland. For 

 this reason the saliva which first begins to flow contains 

 ptyalin and mucin, because these elements were stored up 

 in the gland and were then washed out. But as soon as 

 this stored supply is exhausted nothing but the transuda- 

 tions continue. These transudations may, then, flow from 

 the gland for an indefinite period, because as the blood 

 supply in the gland is kept constant the source from which 

 the transudations are derived does not diminish. When, 

 finally, such a gland stops secreting it is probably more a 

 nervous exhaustion than a glandular one. This will ex- 



