74 PHYSIOLOGY CHAP. 



So, too, it may be held that the peripheral stimulus for thirst 

 consists in the dryiiess of the mucous memhraue of the mouth and 

 pharynx, which causes physico-chemical changes in the epithelia, 

 which again excite the terminations of the corresponding sensory 

 nerves. 



By what paths arc the peripheral excitations of hunger trans- 

 mitted to the centres ? It has been shown in numerous experi- 

 ments on fasting animals by Sedillot, Schiff, Longet, and Beaunis 

 that the sensation of hunger persists after section of the vagi in 

 the neck and also below the diaphragm. Brachet (1834), how- 

 ever, on starving a dog for 24 hours saw that section of the 

 vagi, performed after ascertaining that the animal was ready to 

 devour the food presented to it, ipso facto arrested the desire to 

 eat. But he took no account of the depressing effects of pain, and 

 did not note how long the inhibition lasted, nor when hunger set 

 in again. 



We have recently attempted to repeat Brachet's experiment 

 under more favourable conditions, si nee it is so far as we know- 

 unique hi the whole literature of physiology. Two young dogs, 

 each weighing 4500 grins., were kept fasting for 24 hours. We 

 then, under chloroform, exposed and dissected out both vagi at 

 the root of the neck, and passed an aseptic thread round them, 

 so that the nerves could easily be drawn out and divided; the 

 edges of the wound were then sewn l oget her. While waiting for 

 the effects of the chloroform to wear off, and to increase hunger, 

 the two dogs operated on were kept in a cage with a trough 

 containing wain- only. After 48 hours' starvation for the one 

 animal and 7'2 hours for the other, both vagi were cut, under 

 cocaine, to avoid any pain. Previous to this operation both 

 dogs were very hungry. When shown a bit of meat they eagerly 

 tried to seize it, and snatch it from one's hand. Immediately after 

 the nerves had been divided they ran about the room as vigorously 

 as before ; but when meat was offered them, they rejected it, after 

 sniffing and licking it. This condition of absolute loss of 

 appetite began to pass off in the first dog (2 days' starvation) 

 after 40 minutes, in the second (3 days' starvation) after 

 2 hours. On repeating the test in the succeeding hours, the 

 appetite of both dogs was found to be increasing gradually, until 

 it reached the stage of acute hunger, to judge from the avidity 

 with winch the animals devoured meat and bones. 



These experiments, which complete the too long neglected 

 work of Brachet, seem by their simplicity to be of no little value 

 to the theory of the genesis of hunger. They show, not (as 

 Brachet thought) that the sensory branches of the vagus are the 

 only means of transmitting the excitations of hunger to the 

 centres, but that they undoubtedly represent the most excitable 

 paths for these impulses. They further prove indirectly that the 



