INFLUENCE OF THE NERVOUS SYSTEM. 235 



through which the sense of thirst is chiefly derived, are more sen- 

 sitive to this condition of the blood than other nerves are. And 

 the cases of hunger and thirst are not the only ones in which 

 the mind derives, from certain organs, a peculiar predominant 

 sensation of some condition affecting the whole body. Thus, 

 the sensation of the " necessity of breathing," is referred es- 

 pecially to the lungs ; but, as Volkmann's experiments show, 

 it depends on the condition of the blood which circulates every- 

 where, and is felt even after the lungs of animals are removed ; 

 for they continue, even then, to gasp and manifest the sensa- 

 tion of want of breath. And, as with respiration when the 

 lungs are removed, the mind may still feel the body's want of 

 breath ; so in hunger and thirst, even when the stomach has 

 been filled with innutritions substances, or the pneumogastric 

 nerves have been divided, and the mouth and fauces are kept 

 moist, the mind is still aware, by the more obscure sensations 

 in other parts, of the whole body's need of food and water. 



The influence of the nervous system on the secretion of gastric 

 fluid, is shown plainly enough in the influence of the mind 

 upon digestion in the stomach ; and is, in this regard, well 

 illustrated by several of Dr. Beaumont's observations. M. 

 Bernard also, watching the act of gastric digestion in dogs 

 which had fistulous openings into their stomachs, saw that on 

 the instant of dividing their pneumogastric nerves, the process 

 of digestion was stopped, and the mucous membrane of the 

 stomach, previously turgid with blood, became pale, and ceased 

 to secrete. These, however, and the like experiments showing 

 the instant effect of division of the pneumogastric nerves, may 

 prove no more than the effect of a severe shock, and the fact 

 that influences affecting digestion may be conveyed to the 

 stomach through those nerves. From other experiments it 

 may be gathered, that although, as in M. Bernard's, the division 

 of both pneumogastric nerves always temporarily suspends the 

 secretion of gastric fluid, and so arrests the process of digestion, 

 and is occasionally followed by death from inanition ; yet the 

 digestive powers of the stomach may be completely restored 

 after the operation, and the formation of chyme and the nutri- 

 tion of the animal may be carried on almost as perfectly as in 

 health. 



In thirty experiments on Mammalia, which M. Wernscheidt 

 performed under Miiller's direction, not the least difference 

 could be perceived in the action of narcotic poisons introduced 

 into the stomach, whether the pneumogastric had been divided 

 on both sides or not, provided the animals were of the same 

 species and size. It appears, however, that such poisons as are 

 capable of being rendered inert by the action of the gastric 



