HIBERNATION OF MAMMALS — MATTHEWS 415 



During hibernation the blood itself is altered in composition. Ex- 

 periments on hedgehogs have shown that in hibernation the amount 

 of sugar in the blood is less than half that present when the animal is 

 active, but the amount of magnesium is more than twice as great. 

 It has further been found that if active hedgehogs in summer are 

 injected with insulin, which decreases the amount of blood sugar and 

 increases the magnesium, and are placed in a low temperature (but 

 above freezing) an artificial hibernation is induced which may last 

 for many days. When such animals are later removed to a warm 

 temperature they awaken in a normal manner and return again to 

 the warm-blooded state. 



There seems to be some doubt about the temperature of the body 

 during liibernation, for most observers have recorded very low figures 

 by taking the rectal temperature ; but if the temperature of the blood 

 within the heart is measured, an operation that can be done with a 

 small thermocouple mounted in a fine hypodermic needle, much higher 

 values are found. There appears to be a temperature gradient, the 

 extremities being very cold but the center remaining considerably 

 warmer. It is interesting to note in this connection that when non- 

 hibernating animals have been subjected to great cooling, and reduced 

 to torpor, they can be brought back to life only if the heart is warmed 

 first while they are being revived. 



CYCLIC CHANGES IN GLANDULAR ACTIVITY 



In view of the great changes in the blood sugar during hibernation, 

 and of the possibility of inducing an artificial hibernation by the 

 administration of insulin, it is not surprising that striking cyclic 

 changes have been found to occur in the insulin-producing gland of 

 hibernatory animals — the islets of Langerhans in the pancreas. The 

 pancreas produces a digestive secretion that is poured into the intes- 

 tine through the pancreatic duct, but in addition it serves an endocrine 

 function. Certain bunches of cells in its structure do not produce the 

 fluid that is conveyed to the intestine through the duct, but manu- 

 facture substances that pass directly into the blood and have an effect 

 on other parts of the body at a distance when carried to them by the 

 blood stream. These clusters of cells form the islets of Langerhans, 

 and one of their chief functions is the production of insulin, the sub- 

 stance that has such a profound effect upon the metabolism of carbo- 

 hydrates in the body — if insulin is deficient in quantity the amount 

 of sugar in the blood rises to an abnormal level which may be so great 

 that the animal passes into a diabetic coma that terminates fatally. 

 During hibernation there is a great hypertrophy of the endocrine 

 tissue in the pancreas, the proportion of insulin-producing cells 

 present being much greater than during the summer. But the islets 



