November 6, 1885.] 



SCIENCE. 



403 



hour ; the old mouse, in less than three hours. 

 Had these mice, after their first removal, when 

 replaced in the field, dnectly become stupid or 

 actually dormant, it might naturally be inferred 

 that the heat had seriously affected them ; but, as 

 "we have seen, such was not the case. During the 

 evening of the day following my replacing them 

 in the field," the an became cooler by twenty-nine 

 degrees, by 7 P. M., and was thirty-four degrees 

 cooler four hours later ; and the mice were active 

 and fed heartily upon bread crumbs placed near 

 then nest. Now, why, it may be asked, did they 

 not seek out a cooler retreat in the woods near by ? 

 I can only suggest that the supposed sestivating 

 condition was not inconvenient or unpleasant, and 

 that it was preferable to the abandonment of their 

 nest, which was suited to their needs for all time, 

 except such extraordinary spells of hot weather. 

 Either these mice were excessively stupid, or a 

 dormant condition, caused by excessive heat, was 

 nothing unusual with them. 



There is, in this instance, a marked difference 

 from a hibernating sleep, in that the period of dor- 

 mancy was of but a few hours duration ; but was 

 like the torpid slumber of a hibernating animal, in 

 that the condition was one from which it was not 

 possible to arouse them, as from ordinary slumber. 

 The awakening had to come from a change of 

 temperature, and just in proportion as the evenings 

 were warm, the mice were tardy in returning to 

 consciousness. To more effectually test this, I 

 carefully removed these mice from the field, and 

 placed them near a stove, so that the midday tem- 

 perature could be maintained. The result was the 

 continuance of the dormant condition for eighty- 

 four hours. 



When the effect of a protracted drought and 

 heated terms upon our animals has been more fully 

 worked out, I beheve it will be found that many a 

 mouse and other small mammal which is found 

 lying dead as supposed, is really not in a moribund 

 but dormant condition, and if left undisturbed, 

 would revive. But what other evidence is there 

 of this ? The white-footed mice are not, of them- 

 selves, sufficient to prove that aestivation is an es- 

 tablished habit. What other evidence among 

 mammals have we ? 



In August, 1880, I found bats on four different 

 occasions, all of which were apparently in full 

 health, yet they did not, for some reason, which I 

 supposed to be excessive heat then prevailing, 

 resume, at sundown, their crepuscular flights at 

 the usual hour. These bats had ' gone to roost ' 

 under leaves on trees and a grape-vine, and were, 

 no doubt, fully intending to resume their activity 

 after the nap of a day's length was over. Why 

 did they not ? The following days were excessively 



hot, until the fourth, which was a few degrees 

 cooler. It clouded over early in the afternoon ; 

 soon it became damp, and just before the com- 

 mencement of a passing shower, these bats were 

 stirring a little, as they hung. Quivering their 

 wings, as though to see if aU was in working 

 order, and then, away they flew, after, in each 

 case, nearly ninety hours of rest. Does it ade- 

 quately explain aU the facts to say that these bats 

 were overcome by the heat ? They were resting in 

 the shade during the whole day, and the nights, 

 when they would be active, were cooler ; but in 

 these cases, very little cooler. They were nights 

 to be remembered for their sultriness, and may it 

 not be, that there was not sufficient difference in 

 the midday and evening temperature to enable 

 them to throw off the nervous prostration caused 

 by the heat of the day ? Explain it thus, and then 

 we are left to consider what is this nervous pros- 

 tration ? In the case of the bats mentioned, they 

 were aU in a perfectly torpid state, and gave not 

 the least sign of life when handled ; and only 

 flinched slightly, when wounded by being pricked 

 with a needle. Would not nervous prostration 

 that produced insensibility, lasting several hours, 

 almost certainly produce death ? In the case of 

 the bats, a torpid condition of ninety hours pro- 

 duced no iU effects. I am disposed to beheve that 

 the coming hot and dry weather was anticipated, 

 and these bats retired for the purpose of escaping 

 it, and entered into a condition widely different 

 from ordinary sleep, which was to last until the 

 so-called heated term was over, the lowering of the 

 temperature being the one means through which 

 they would be restored to consciousness. There 

 occurs this deliberate action on the part of certain 

 mammals, which regularly hibernate — why should 

 not the same be true of them when the extreme is 

 one of heat, instead of cold ? 



As bearing upon this question, let me quote a 

 few lines from the Encyclopedia Brittannica — 

 ninth edition — article, Hibernation. It says : " The 

 dormouse not only hibernates in the sti'ict sense of 

 the term, but wiU sleep at intervals for several 

 days together, during mild weather. When a 

 Myoxus, an aUied animal inhabiting Africa, was 

 brought to Europe, it hibernated as if this were its 

 normal habit. Whether it sestivates in its native 

 country is not known, but its liibernating in 

 Europe shows a greater power of adapting itself 

 to changed conditions of life than we should have 

 been inchned to suspect." 



I would briefly call attention to two points in 

 the above : that in temperate chmates prolonged 

 sleep is not unknown among rodents ; and also, 

 that some tropical rodents probably gestivate. In 

 the case of the white-footed mice, and, too, of the 



