450 THE HUMAN BODY. 



is, within a degree, the same in winter or summer; within 

 the arctic circle or on the equator. 



Moderate warmth accelerates protoplasmic activity; com- 

 pare a frog dormant in the winter with the same animal 

 active in the warm months: what is true of the whole 

 frog is true of each of its living cells. Its muscles contract 

 more 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 amoeboid movements than they do at the tempera- 

 ture 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, a.s 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 therefore the amount 

 of oxygen it needs, depend to a great extent upon the tem- 

 perature of the medium in which it is living. With the 

 warm-blooded animal the reverse is the case. It always 

 keeps up its temperature to that at which its tissues live 

 best, and accordingly in cold weather 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. In fact the living tissues of a man 

 may be compared to hothouse plants, living in an artifici- 

 ally 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 tem- 

 perature no matter whether it be in cold or warm surround- 

 ings, 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 



