96 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



poiesis in the spleen and no erythropoiesis in the bone marrow of hibernating 

 woodchucks.** 



Many investigators who have worked on hibernation have noted that the blood 

 of animals which are hibernating is very slow to clot and Svihla, ct aL,'^°~ and 

 Suomalainen and Lehto^°® have shown this to be the case in aestivating ground 

 squirrels and hibernating hedgehogs respectively. Svihla, et al.,^°^ indicated that 

 the slowness in clotting is due to a lack of prothrombin, but they give no body tem- 

 peratures or temperatures of the blood, so that the effects of blood temperature 

 per se cannot be separated from the effects of lack of prothrombin. 



Suomalainen^'' found a high serum magnesium in hibernating hedgehogs as did 

 jMcBirnie, et al./^ with woodchucks, but the former reports a low serum potassium 

 while the latter found it high during hibernation. ''■"'■ Suomalainen^^ has reviewed 

 the earlier contradictory results on serum calcium and reports very little difference 

 in the awake and hibernating hedgehog. Kayser^^ has thoroughly reviewed the 

 changes in electrolytes and vitamins during hibernation and the interested reader 

 is referred to his paper. 



Growth. Growth during hibernation is greatly suppressed. ^^"' ^" On the other 

 hand, there must be some organ growth during the total hibernating period, for 

 Foster*^ showed that female ground squirrels breed less than five days after coming 

 out of hibernation in the spring. Rasmussen*^ (confirmed by Brace^"") found slight 

 changes in the gonads of the male woodchuck and greater changes*'^ in the female 

 before the end of hibernation. It is not clear, however, that these changes did not 

 take place during the brief periods when the animal was awake. That the tempera- 

 ture of the tissues, rather than a lack of growth stimulus, is the factor which cur- 

 tails growth during hibernation was shown by Lyman and Dempsey^^- by injecting 

 testosterone into castrated, hibernating golden hamsters. In spite of the presence 

 of a stimulus which caused enlargement of the seminal vesicles in the awake animals, 

 there was no change in the animals which hibernated more than 7 days of the 

 10-day test period (fig. 10). Lyman and Fawcett^^^ have shown that homologous 

 methylcholanthrene-induced sarcoma grafts in the hamster cheek pouch fail to grow 

 during hibernation but are still viable and capable of proliferation when the body 

 temperature returned to 37° C. after periods of hibernation lasting as long as 

 55 days (fig. 11). Courrier^^* found that Wallerian degeneration proceeds more 

 slowly in hibernating serotine bats than in awake animals. Smith and Grenan^^^ have 

 shown that death from X-ray irradiation is greatly delayed in the woodchuck if the 

 animal is hibernating, but that death occurs soon after the animal wakes from hiber- 

 nation. This has been confirmed by Doull and Dubois^^*^ using the ground squirrel. 



**W. Z. Lidicker, Jr. and W. H. Davis (Proc. Soc. Exp. Biol, and Med. 59.- 640, 1955) 

 have confirmed earlier reports tliat the spleen in bats is greatly enlarged during hibernation and 

 have correlated this with a marked decrease in the number of circulating erythrocytes. During 

 the waking process, the engorged spleen released the erythrocytes into the blood stream. On the 

 other Iiand, V. P. Raths (Zeitschr. f. Biol. 106: 109, 1953) using the European hamster, and 

 P. Suomalainen and T. Granstrom (Exp. Cell Res., Suppl. 3: 335, 1955) using the golden 

 hamster, both report an increase in total hemoglobin and in the number of circulating erythro- 

 cytes in animals during hibernation. They also show a similar, though not so large hcmocon- 

 centration in animals exposed to cold but not in hibernation. It seems very probable tliat I)ats 

 differ from other hibernators in this respect. 



tt Recently, M. L. Riedesel and G. E. Folk, Jr. (Am. J. Physiol. 179: 665, 1954) report a 

 50% increase in serum magnesium after only 42 hours of hibernation in bats. Serum calcium 

 level was slightly decreased and serum potassium remained unchanged. 



