478 THE HUMAN BODY, 



rapidly when warmed, and the white corpuscles of its blood 

 when heated up to the temperature of the Human Body are 

 seen (with the microscope) to exhibit much more active amoe- 

 boid movements than they do at the temperature of frog's 

 blood. In summer a frog or other cold-blooded animal uses 

 much more oxygen and evolves much more carbon dioxide 

 than in winter, as shown not only by direct measurements of 

 its gaseous exchanges, but by the fact that in winter a frog 

 can live a long time after its lungs have been removed (being 

 able to breathe sufficiently through its moist skin), while in 

 warm weather it dies of asphyxia very soon after the same 

 loss. The warmer weather puts its tissues in a more active 

 state; and so the amount of work the animal does, and there- 

 fore the amount of oxygen it needs, depend to a great extent 

 upon the temperature of the medium in which it is living. 

 With the warm-blooded animal the reverse is the case. Within 

 very wide limits of exposure to heat or cold it maintains its 

 temperature at that at which its tissues live best ; accordingly 

 in cold weather it uses more oxygen and sets free more carbon 

 dioxide because it needs a more active internal combustion to 

 compensate for its greater loss of heat to the exterior. And 

 it does not become warmer in warm weather, partly because 

 its oxidations ore less than in cold (other things being equal), 

 and partly because of physiological arrangements by which it 

 loses heat faster from its body. In fact the living tissues of 

 a man may be compared to hothouse plants, living in an arti- 

 ficially maintained temperature; but they differ from the 

 plants in the fact that they themselves are the seats of the 

 combustions by which the temperature is kept up. Since, 

 within wide limits, the Human Body retains the same temper- 

 ature no matter whether it be in cold or warm surroundings, 

 it is clear that it must possess an accurate arrangement for 

 heat regulation ; either by controlling the production of heat 

 in it, or the loss of heat from it, or both. 



The Temperature of the Body. The parts of the Body 

 are all either in contact with one another directly or, if not, 

 at least indirectly through the blood, which, flowing from 

 part to part, carries heat from warmer to colder regions. 

 Thus, although at one time one group of muscles may espe- 

 cially work, liberating heat, and at other times another, or 

 the muscles may be at rest and the glands the seat of active 

 oxidation, the temperature of the whole Body is kept pretty 

 much the same. The skin, however, which is in direct con- 



