ANIMAL HEAT. 



661 



the interior being prevented from escaping by 

 means of a circular pad of soft napkins placed 

 between the edge of the outlet and the neck. 

 The temperature of the mouth, in this^way, if it 

 was increased, must be increased in consequence 

 of a rise of temperature in the parts of the body 

 included in the bath . After a stay of seventeen 

 minutes in the bath, heated from 37, 5 to 

 48, 75 c. (99 to 120 F.), the temperature of 

 M. Delaroche's mouth rose 3, 12 c. Under 

 similar circumstances, the temperature of the 

 bath being from 40 to 41, 25 c. (104 to 

 106 F.), the temperature of M. Berger's mouth 

 increased 1. 7 c. in the course of fifteen 

 minutes. 



It is pretty obvious that experiments upon 

 the human subject cannot be pushed far enough 

 to ascertain the highest amount of temperature 

 that can be acquired under the influence of 

 exposure to air of excessively high tempera- 

 ture. To judge of this analogically, recourse 

 must be had to warm-blooded animals of the 

 two classes, Mammalia and Birds. Messrs. 

 Delaroche and Berger consequently exposed 

 different species of Mammalia and Birds to dry 

 hot air of different temperatures, from 50 to 

 93, 75 c. (122 to 201 F.), leaving them im- 

 mersed till they died. The whole of the ani- 

 mals that were made subjects of experiment, 

 in spite of diversity of class and species, and 

 of the varieties of temperature to which they 

 were exposed, had gained an increase of tem- 

 perature nearly equal at the moment of their 

 death. The limits of the variations being be- 

 tween the terms 6, 25 and 7, 18 c., the amount 

 of difference did not exceed 0, 93 c. which is a 

 very trifling quantity . It may therefore be inferred 

 that man and the warm-blooded animals cannot, 

 under the influence of exposure to dry air of 

 excessively high temperature, have the heat of 

 their body raised during life to a greater extent 

 than from 7 to 8 c. The temperature of the 

 body being increased to this extent becomes 

 fataf. It is in fact only attained at the moment 

 of dissolution ; perhaps death has virtually 

 taken place before it is attained. 



We have seen that Franklin observed the 

 temperature of his body to be lower than that 

 of the air on a very hot day. Such a circum- 

 stance is rare in what may be called natural con- 

 ditions as regards man and the warm-blooded 

 animals ; inasmuch as it rarely happens that 

 the temperature of the air surpasses that of 

 their bodies generally. The case is different, 

 however, as regards the cold-blooded tribes. 

 It is not at all necessary that the temperature 

 of the air be very high to afford opportunities 

 of observing the phenomenon in question 

 among cold-blooded animals. This was ob- 

 served for the first time by Sir Charles Blagden 

 in a frog, which on a summer's day, when the 

 heat was by no means excessive, he observed to 

 be lower in temperature than the surrounding 

 air. A fact of this kind could not remain 

 isolated and unconnected with others. Accord- 

 ingly we observe among the experiments of 

 Dr. Davy such facts as the following : The 

 temperature of the atmosphere being 32 c. 

 (90 F.), that of a tortoise was only 29, 4 



(85 F.). The air marking 26, 7 (80 F.), 

 a frog indicated 25 (77 F.). The air being at 

 28, 3 (83 F.), the blatta orientalis was at 

 23, 9 (75 F.). The air at 26, 19 c., 

 (79, 5 F.), a scorpion was at 25, 3 (78 F.). 

 It is therefore apparent that the phenomenon is 

 general among animals with cold blood ; that 

 during the highest heats of summer, the tem- 

 perature still falling short of excessive, the heat 

 of their bodies is below that of the air. There 

 is thus a limit of summer temperature which 

 separates two orders of phenomena relative 

 to the temperature of cold-blooded animals. 

 Starting from a mean temperature of the air, 

 that of cold-blooded animals, the vertebrate 

 as well as the invertebrate tribes, is superior to 

 this mean, only varying in this respect within 

 the narrow limits of from a few fractional parts 

 of a degree to about four degrees centigrade, 

 until the air attains the summer heat. Towards 

 this limit the differences decrease, and the 

 term 25 or 26 c. (77 to 79 F.) attained, they 

 become nil. The inverse phenomenon is also 

 observed : the temperature of the greater num- 

 ber is inferior to that of the air, and the dif- 

 ferences go on increasing with the rise in 

 temperature of the external air. 



These phenomena are of great interest in 

 themselves, but of still greater from the light 

 they cast on questions of a similar kind relative 

 to man and the warm-blooded tribes of crea- 

 tion. The slight evolution of heat by the cold- 

 blooded animals rendering their condition more 

 simple, allows us to appreciate distinctly the 

 influence of external causes. 



We now proceed to treat of a third condition 

 influencing temperature, namely, 



Evaporation. : The fluids so far surpass the 

 solids in the bodies of animals that they cer- 

 tainly constitute the larger portion of their 

 masses ; and, further, the exterior surface of 

 animal bodies generally is extremely porous. 

 Animals are consequently subjected to the 

 ordinary physical laws of evaporation. It is 

 very long since, in addition to the sweat or 

 visible perspiration, the existence of an invisible 

 perspiration has been recognized. The latter is 

 owing in great part to the effects of evaporation. 

 Now evaporation cannot take place without the 

 occurrence of cooling or loss of temperature 

 in the ratio of the quantity of vapour formed. 

 Without keeping this cause of refrigeration in 

 view, we should fall into serious mistakes in 

 estimating the heat of animals. If, for ex- 

 ample, we would compare the heat of two 

 animals, which, unwittingly to the observer, 

 should be under different conditions of eva- 

 poration, we should deceive ourselves greatly 

 in regard to their respective temperatures. 



It is even so with reference to another fact 

 bearing upon temperature, which is often forced 

 on the attention, and which has almost always 

 led inquirers into error. There are many ani- 

 mals among the inferior classes of the Inverte- 

 brata, which tried by the thermometer exhibit 

 no difference in temperature from that of the 

 surrounding air. These creatures do not, con- 

 sequently, appear to have any faculty of pro- 

 ducing heat. But in the mere fact of their main- 



