HIBERNATION IN MAMMALS— LYMAN axd CHATFIELD 83 



liasU'iis liilKTuatidii in invdund s(|uirii-ls, and \\c liavc found the sanic tn he tine for 

 woodchucks in our laboratory. On the otlicr hand, as might be expected in an animal 

 which depends on stored fond, starvation never brings on hibernation in the 

 hamster.-' 



Wade-'^ has reported that ground scjuirrels can gain weight very rapidly when 

 given an unlimited supply of food and believes this is a characteristic of hibernators. 

 Wilber and Musacchia-" measured the lipids of liver and kidney in arctic ground 

 stjuirrels trapi)ed in July and September. The higher concentration of fatty acid, 

 lipid phosphorus and phospholipid in specimens caught during July indicated a rapid 

 fat turnover at this time, with a slower lipid metalxjlism as the animals approached 

 the hibernation period in late September. Although it is a fruitful avenue of re- 

 search, an exhaustive study of the relation of adipose tissue to hibernation has yet 

 to be made, though the role of brown fat has been the object of some research and 

 much speculation. 



Recently Fawcett and Lyman-' examined the depot fat in regard to its utilization 

 during hil)ernation. Since many of the animal fats are solid at 5° C, the question 

 wdiether solid or semisolid fat can be used by a hibernator is an interesting one. It 

 was shown that exposure to cold (5° C. ) caused hamsters to desaturate their dejxjt 

 fat, raising the iodine number about five points and thus lowering the melting point 

 to some extent. A diet of 20% saturated fat caused the iodine number to decline 

 17 points in animals maintained at room temperature, but only 10 points in animals 

 exposed to cold. Similarly, hamsters fed a diet rich in unsaturated fat showed a 

 small increase of the iodine number at room temperature but a further increase of 

 about five points was found in the animals exposed to a cold environment. Although 

 the fat of animals at room temperature on a saturated fat diet was sufficiently satu- 

 rated to be solid when tested //; vitro at 5° C, the increased unsaturation of the fat 

 in the animals exposed to cold permitted them to maintain their fat in a liquid or 

 semiliquid state at the hibernating temperature of 5° C. It was further shown that 

 the albino rat, which is incapable of hibernation, did not desaturate its fat when ex- 

 posed to a low environmental temperature no matter what the diet (fig. 1 ) . Thirteen- 

 lined ground squirrels fed the same diet as hamsters had an iodine number of ap- 

 proximately 93 compared with a value of 88 in hamsters. The diet of saturated fat 

 which increased the saturation in hamsters had no effect on the saturation of the fat 

 of ground squirrels under the same conditions. The effect of cold on the ground 

 squirrels' fat could not be determined because the ground s(|uirrels entered hiberna- 

 tion too rapidly after exposure to cold. 



In the case of the hamster, there is a long period after exposure to cold before 

 the animal enters the hibernating state and during part of this time, at least, the fat 

 is evidently l)eing changed to a less saturated form. The depot fat of ground squirrels 

 is more unsaturated at the outset and these animals enter hibernation in a much 

 shorter time when exposed to cold. It is tempting to postulate that the delay in hiber- 

 nation in the hamster has some relationship to the saturation and melting point of 

 the fat. However, it has not been possible to shorten the period between exposure 

 to cold and hibernation Ijy feeding hamsters an unsaturated fat diet, nor to prevent 

 or curtail hibernation by feeding them a saturated fat diet. Therefore, though the 



