530 INFLUENCE OF CLIMATE 



evaporation, and returning to their source by 

 rivers, the blood is conveyed with immense ra- 

 pidity from the lungs and heart throughout the 

 system, renewing its composition by the deposi- 

 tion of fresh organic molecules, the cohesion of 

 which diminishes until the cause of force is ex- 

 panded by action ; when they are removed by 

 absorption, conveyed into the general circula- 

 tion, and thence out of the body by elimination. 

 Not a particle remains quiescent for any con- 

 siderable time, so that in about forty days, a 

 complete revolution is supposed to be effected 

 in its substance, if we except the cartilages, 

 bones, and teeth, the last two of which are almost 

 wholly destitute of life. The cellular tissue is 

 also endowed with a very low degree of vital 

 energy, compared with the nervous and muscular, 

 if we except the mucous membranes ; and con- 

 tains much less nitrogen in its composition. 



That the power of living bodies to renew their 

 composition by assimilation, and to reproduce their 

 species by generation, is governed by the emphatic 

 agency of caloric, is evident from the fact, that the 

 power of nature to multiply organic forms, is di- 

 rectly in proportion to the temperature of the 

 earth, from the equator to the polar circles. It is 

 only in the regions of perpetual summer, that 

 the number of species, variety of structure, and 

 magnitude of form, are developed in full per- 

 fection throughout the vegetable world where 



