ANIMAL HEAT. 



669 



winter the temperature of the air is lower ; in 

 summer the amount of evaporation greater. 

 These two conditions of refrigeration, therefore, 

 tend to compensate one another, and conse- 

 quently to maintain the equilibrium of tempe- 

 rature as regards the body in the two opposite 

 seasons. They have unquestionably a consi- 

 derable share in this business; and it was long 

 believed that the simple difference indicated in 

 the external conditions sufficed to preserve the 

 temperature of the body alike during the two 

 periods. But in reflecting on the phenomena 

 presented by cold-blooded animals with the 

 changes of the seasons, which have already 

 been spoken of at length, we find such an opi- 

 nion or view to be inadmissible. For in ex- 

 amining those species of cold-blooded animals 

 which from their structure are liable to lose 

 more by evaporation than any other animal, 

 we see that no such compensation takes place. 

 Frogs, for example, the skin of which is so soft 

 and permeable, and whose bodies besides are 

 so succulent that they must be presumed in the 

 most favourable circumstances to sustain loss 

 by evaporation, ought to preserve the same 

 temperature in winter and in summer if the 

 low temperature in winter were compensated 

 by the excess of evaporation in proportion as 

 the heat of the season augments. But we 

 know that the temperature of these creatures 

 follows, to a very great extent, that of the at- 

 mosphere, between and 25 c. (32 and 77 

 F.), differing at no time from it by more than a 

 degree or two. The phenomenon here is sim- 

 ple, by reason of the slight evolution of 

 caloric by the frog, and leaves no doubt upon 

 the mind. We must, therefore, have recourse 

 to other conditions, in order to explain the 

 slight difference that is observed in the summer 

 and winter temperature of man and other warm- 

 blooded animals. Since external conditions 

 do not appear to explain the phenomena, it 

 must undoubtedly mainly depend oncertain 

 changes effected in the animal itself. Now, 

 since the internal conditions which influence 

 the temperature of the body are those also that 

 regulate the production of heat, it is here that 

 the change must be effected. 



It is obvious that the cause of refrigeration 

 in winter being more active, to meet the greater 

 expenditure there must be the means provided 

 for furnishing a larger supply the calorific 

 faculty must be more active in winter than in 

 summer. The inverse of this takes place in 

 summer; so that the temperature of the body 

 in the two seasons is determined in the follow- 

 ing manner: in winter there is a more active 

 production with a greater loss ; in summer a 

 less production, with a smaller /ossof heat. In 

 this way is there compensation, and a perfect 

 equilibrium maintained at all seasons. To 

 render this relation more evident, it may be 

 expressed in another manner ; as, for example, 

 in summer the body receives more heat from 

 without, and produces less ; in winter it receives 

 less and produces more. 



These considerations carry us farther. As 

 this difference in the production of heat lasts as 

 long as the various seasons, and takes place 



progressively, it is to be presumed that it be- 

 longs to an intimate and more or less en- 

 during change effected in the state of the 

 body. In other words, the constitution alters, 

 and the faculty of producing heat changes in 

 the same degree. The fact thus expressed is 

 immediately susceptible of an interesting ap- 

 plication. If the faculty of producing heat is 

 less in summer, the temperature of the body 

 will not be maintained to the same point in the 

 two seasons under sudden exposure to the 

 same degree of cold. By subjecting animals 

 to the test of experiment in the two seasons, it 

 is easy to judge of the justice of the preceding 

 deductions, as well as of the principles which 

 led to them. To have the mode of refrigera- 

 tion precisely the same, attention must be had 

 not merely to the thermometric temperature of 

 the air, but also to its humidity, which ought 

 to be the same in both instances. A difference 

 in the hygrometrie state of the air will certainly 

 produce a difference in the effects of refrigera- 

 tion. The apparatus employed consisted of 

 earthen vessels plunged amidstaquantity of melt- 

 ing ice. Air thus cooled soon reaches the point 

 of extreme humidity. The air being at zero c. 

 (32 F.), the animal is introduced, placed upon 

 a stage of gauze to prevent its coming in con- 

 tact with the moist and rapidly conducting 

 surface of the vessel. A cover, also piled over 

 with ice, is then placed over the apparatus, but 

 so arranged as still to permit the ready reno- 

 vation of the air contained in the interior. 

 Still farther to secure the purity of the included 

 air, a solution of potash, which of course ab- 

 sorbed the carbonic acid produced with avidity, 

 occupied the bottom of the vessel. In winter, 

 in the month of February, the experiment was 

 made at the same time upon five adult spar- 

 rows, which were all included in the apparatus. 

 At the end of an hour they were found one 

 with another to have lost no more than 0, 4 c., 

 or less than half a degree; some of them 

 having suffered no depression of temperature 

 whatsoever, others having lost as much as, but 

 none more than, 1 c. The temperature of the 

 whole then remained stationary to the end of 

 the experiment, which was continued for three 

 hours. In the month of July the same expe- 

 riment was performed upon four full-grown or 

 adult sparrows. The temperature of these 

 birds at the end of an hour had undergone a 

 depression, the mean term of which was 3, 

 62, and the extremes 6, 5 and 2 c. At the 

 end of the third hour the mean term of the 

 refrigeration suffered was 6, the extremes being 

 12 and 3, 5 c. It ought to have been stated 

 that in the experiment in the winter month, 

 the birds had been for some time kept in a 

 warm room, so that the sudden transition was 

 the same in both instances, in the winter as 

 well as the summer experiment. The diver- 

 sity in the constitution of these birds, conse- 

 quently, with reference to the powers of pro- 

 ducing heat, was an effect of the difference of 

 the seasons. Each month the temperature of 

 which differs in any degree from that of the 

 month before or after it, has an obvious ten- 

 dency to modify the temperament or constitu- 



