540 THE HUMAN BODY 



perature of the Human Body are seen (with the microscope) to 

 exhibit much more active amoeboid 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 dioxid than in winter, as shown not only by direct meas- 

 urements 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 therefore 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 expo- 

 sure 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 dioxid 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 are less than in cold (other 

 things being equal), and partly because of physiological arrange- 

 ments 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 artificially 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 tempera- 

 ture no matter whether it be in cold or warm surroundings, it is 

 clear that it must possess an accurate arrangement for heat reg- 

 ulation; 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 in- 

 directly 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 especially 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, 



