The Animal Body — Digestion — Metabolism. 31 



tite, and palatability. Pawlow and his associates performed the 

 following surgical operations on dogs: (1) The ducts or tubes which 

 deliver the saliva into the mouth were cut, turned outward, and 

 healed into the cut edges of the skin, so that when saliva was se- 

 creted it poured out thru the opening and could be caught in glass 

 tubes attached to the dog's head. (2) The gullet, which carries 

 food from the mouth to the stomach, was cut across, led outward, 

 and healed in the skin at the throat, so that when food was swal- 

 lowed it would pass out at the severed end and fall back into the 

 dish out of which he was feeding. Food so eaten was called a 

 "false meal." In many eases a dog with a gullet thus severed 

 would chew and swallow the "false meal" again and again with 

 apparent satisfaction. (3) An opening was made thru the side of 

 a dog and into his stomach. On the healing of the stomach wall 

 with the cut in the skin, the investigator was enabled to pass food 

 directly into the stomach and study the processes of digestion oc- 

 curring within that organ. (4) A portion of the stomach was con- 

 stricted and made into a small separate chamber, which likewise 

 opened out thru the side of the dog. Here the flow of juices could 

 be studied independent of admixture with food placed in the other 

 portion of the stomach. (5) The small intestine was drawn to the 

 side of the dog, and an opening made in it the same as in the stom- 

 ach. (6) The pancreatic duct was cut and led outward, so that 

 its secretion could likewise be studied. 



Many persons assisted in these operations, and many dogs were 

 used in the various studies. The animals usually yielded readily 

 to the operations and lived comfortable lives, so that the results 

 were normal. 



It was found that the character, composition, and quantity of 

 saliva secreted varied greatly according to the composition, quality, 

 and other characteristics of the food rather than according to either 

 appetite and hunger, or to the palatability of any particular food. 



It was found that when food was placed directly in the stomach 

 it did not necessarily call forth the gastric secretions from the walls 

 of the stomach. On the other hand, the sight, smell, or taste of 

 food not only started the flow of saliva in the- mouth, but the gas- 

 tric juices also began to pour from the walls of the stomach even 

 when there was no food in that organ. Neither chemical nor me- 

 chanical stimulation of the mucous membrane of the mouth was 

 capable of reflexly starting a flow of the juices of the stomach. The 

 gastric secretions which are brought forth by the sight, taste, or 



