138 NATURE AND LIFE. 



transformed into motion. It is partly wasted by transpira- 

 tion through the skin, by touch, and especially by radiation ; 

 it is used in keeping up to a constant point the temperature 

 of the animal, subjected to many causes of refrigeration. 



The mechanical labor performed by an animal is very 

 complex. Independently of visible muscular motions, there 

 are all the changes of place in the interior organs, the con- 

 tinual passage of the blood, the contractions and dilata- 

 tions of a great number of parts. Now, these actions are 

 only possible in so far as the phenomena of breathing are 

 taking place in the active region. Prevent arterial blood 

 from coming to the muscle, that is to say, prevent combus- 

 tion taking place, and consequent heat evolving in it, 

 and, although the structure of the organ suffers no harm, 

 it loses its contractile power. Mere compression of the 

 supplying artery of the muscle, so as to check the flow of 

 blood in it, causes the organ to grow cool and lose its power. 

 The labors of Hirn and Be"clard have clearly established 

 the relations between heat and muscular motion. Later ex- 

 periments by Onimus have fixed, with equal precision, the 

 efficiency of heat through the movements of circulation. 



We have said that the heat-producing power of ali- 

 ments will be the more considerable in proportion as they 

 contain a greater quantity of elements that need a large 

 supply of oxygen for their combustion. Therefore, meat 

 and fats repair the losses of the system much more speedi- 

 ly than vegetable substances. The latter are suitable for 

 the inhabitants of warm countries who do not require to 

 produce heat, which the atmosphere supplies them with 

 abundantly. The inhabitants of cold regions, on the con- 

 trary, whose accessions of heat ought to be as continual as 

 energetic, are urged by instinct to use meats and fats, which 

 throw out great heat in their combustion. For instance, 

 it is a physiological necessity that the Lapps should feed 

 on the oil of cetacea, as it is a necessity for men of the 



