230 



CAUSES OF VARIATION 



freed themselves from the bondage due to the accident of birth- 

 place, being able to move about and therefore to establish in the 

 .widest sense an independent existence. 



Notwithstanding all this, and after making allowance for the 

 grosser influences over lower organisms, the fact yet remains 

 that, to a slight extent, and to a slight extent only, the animal 

 is influenced by the character of his food. That this influence is 

 larger upon the products of the body than upon the body itself 

 is certain ; and upon the subtler qualities, like flavor, rather than 

 the more essentially biological characters such as structure. 



SECTION III THE EFFECT OF MOISTURE UPON 

 DEVELOPMENT 



Animals as a rule are quite independent of moisture, providing 

 their direct needs for water are satisfied in the way of body 

 consumption in addition to that needed to reduce the effects of 

 internal heat by evaporation. 1 



Plants on the other hand do not have the circulatory system of 

 animals, and they depend upon water, taken in by the roots and 

 evaporated by the leaves, to actually carry food to all parts of the 

 structure. Their need for water is therefore far above the amounts 

 necessary for actual composition. For example, it requires the 

 evaporation of something like the equivalent of eight inches of 

 standing water over the entire field to mature an average corn crop. 



1 It is often erroneously taught that animals consume carbonaceous foods to 

 sustain the body temperature, while the truth is that all food actually utilized is 

 broken down and its energy set free. This energy is disposed of in three ways : 

 first, to a slight extent in effecting the recombination of the elements of the food 

 into the exceedingly complex protoplasm of the body or its products ; second, by 

 the body or some of its parts in the form of internal or of external work ; or, third, 

 it is radiated in the form of heat of low intensity. In this way the body is a factory 

 that is constantly producing heat, which must be disposed of or the structure will be 

 destroyed. There are but two ways of doing this, by radiation and by evapora- 

 tion. The body is thus constantly producing and is as constantly losing heat. Its 

 actual temperature is certain to be something above that of the surrounding'medium, 

 how much will depend upon the relation between the rapidity of production 

 and the facilities for radiation and evaporation. The body temperature is thus a 

 kind of algebraic sum, and it depends upon a great variety of conditions. Small 

 animals radiate rapidly, large ones less rapidly, for radiation is a surface action, 

 and their surface is less in proportion to the bulk. Hogs radiate slowly, because 

 of their blanket of fat. They do not sweat, and thus are easily overheated. 



