190 ANIMAL HEAT. 



is not lower than that of younger persons, yet the power of 

 resisting cold is less in them exposure to a low temperature 

 causing a greater reduction of heat than in young persons. 



The same rapid diminution of temperature was observed by 

 M. Edwards in the new-born young of most carnivorous and 

 rodent animals when they were removed from the parent, the 

 temperature of the atmosphere being between 50 and 53$ 

 F. ; whereas, while lying close to the body of the mother, 

 their temperature was only 2 or 3 degrees lower than 

 hers. The same law applies to the young of birds. Young 

 sparrows, a week after they were hatched, had a temperature 

 of 95 to 97, while in the nest ; but when taken from it, their 

 temperature fell in one hour to 66, the temperature of the 

 atmosphere being at the time 622. It appears from his in- 

 vestigations, that in respect of the power of generating heat, 

 some Mammalia are born in a less developed condition than 

 others ; and that the young of dogs, cats, and rabbits, for 

 example, are inferior to the young of those animals which are 

 not born blind. The need of external warmth to keep up 

 the temperature of new-born children is well known ; the re- 

 searches of M. Edwards show that the want of it is, as Hunter 

 suggested, a much more frequent cause of death in new-born 

 children than is generally supposed, and furnish a strong argu- 

 ment against the idea, that children, by early exposure to 

 cold, can soon be hardened into resisting its injurious influ- 

 ence. 



Sex. The average temperature of the female would appear 

 from observations by Dr. Ogle to be very slightly higher than 

 that of the male. 



Period of the Day. The temperature undergoes a gradual 

 alteration, to the extent of about 1 to 1^ F. in the course of 

 the day and night ; the minimum being at night or in the early 

 morning, the maximum late in the afternoon. 



Exercise. Active exercise raises the temperature of the body. 

 This may be partly ascribed to the fact, that every muscular 

 contraction is attended by the development of one or two de- 

 grees of heat in the acting muscle ; and that the heat is in- 

 creased according to the number and rapidity of these con- 

 tractions, and is quickly diffused by the blood circulating from 

 the heated muscles. Possibly, also, some heat may be gene- 

 rated in the various movements, stretchings, and recoilings of 

 the other tissues, as the arteries, whose elastic walls, alternately 

 dilated and contracted, may give out some heat, just as caout- 

 chouc alternately stretched and recoiling becomes hot. But 

 the heat thus developed cannot be great. 



Moreover, the increase of temperature throughout the whole 



