98 COMPARATIVE PHYSIOLOGY 



and Minkowski produced glycosuria (increase of sugar in the 

 urine) by the removal of the pancreas in the dog. Later it 

 was shown that ligation of the pancreatic duct produces 

 degeneration of the acini ; extraction of the islet tissue then 

 yields a product which, when injected into the diabetic dog was 

 found by Banting and Best (1922) to lower the blood sugar, and 

 raise the respiratory quotient. Macleod and his co-workers 

 have shown that extracts of the islet tissues in fishes relieve 

 the diabetes produced by extirpation of the pancreas in rabbits. 

 The exact stage at which insulin, the internal secretion of the 

 pancreas, influences carbohydrate metabolism is still not fully 

 understood. The lowering of the blood sugar produced by in- 

 jection of insulin in mammals is accompanied by convulsions, 

 which can also be reproduced according to Huxley and Fulton 

 (1923) in frogs. Macleod finds that injection of insulin re- 

 duces the blood sugar content in fishes, and that removal of 

 the islet tissue causes hyperglycoemia. 



Absorption and passage of Foodstuffs along the Gut.— The 

 motion of food in the mammalian gut depends upon more 

 than one mode of response on the part of the circular 

 and longitudinal musculature of its wall. There are rhyth- 

 mical movements which tend to churn the food without 

 moving it predominantly in one direction ; these are an 

 intrinsic property of the muscle itself, though subject to 

 inhibitory and excitatory nervous control by the splanchnic 

 and vagus nerves respectively. Further, when mechanically 

 stimulated, intestinal muscle shows a relaxation of tone and 

 inhibition of movement on the aboral side of the point stimxU- 

 lated, accompanied by increased force of movement on the 

 oral side (law of the intestine). This is generally believed 

 to depend on a local nervous mechanism, the myenteric plexus ; 

 its function is to keep the food moving on the whole towards 

 the anal end of the gut. 



The food is propelled along the gut by the contraction of 

 its muscular walls in annelids, molluscs, arthropods, and 

 echinoderms as well as in vertebrates. The intrinsic rhythm 

 of the muscular system of the gut is beautifully seen in the 

 excised alimentary tract of many worms, sea-urchins, and 



