760 General and Applied Biology 



Not all the functions of colorations in plants and animals are known. 

 The complex color-producing mechanism of an animal renders that 

 animal less conspicuous and less likely to be destroyed because of its 

 ''protective coloration." When pigments are located on or near the sur- 

 face, they are usually protective for the sensitive tissues beneath by ab- 

 sorbing certain light waves. Pigments which line the visceral cavity or 

 cover certain nerves of animals also may protect. Albinism (absence of 

 pigment) causes an organism to be very sensitive to light. Human albinos, 

 and even blonds, are more sensitive to light than darker-skinned persons. 

 People in the tropics are heavily pigmented, naturally, or acquire pro- 

 tective pigments in the form of heavy tan. "Freckles" in the human 

 skin are due to the increase in the pigments naturally present when 

 stimulated by light. The interesting and complicated phenomena of the 

 coloration of autumnal leaves have been considered in detail elsewhere. 



Production and Use of Heat 



When any kind of energy is released, there is an accompanying for- 

 mation of more or less heat. In some instances this heat may be used 

 to regulate chemical activities or control the body temperature, while in 

 others the heat is a waste product which is no longer of use to the or- 

 ganism. In the formation of certain chemical compounds, there is often 

 some heat produced. In some instances, such as the spontaneous com- 

 bustion of hay, the amount of heat produced is sufficiently great to start 

 a fire. In the destruction of chemical compounds, usually by oxidation, 

 there is liberated a certain quantity of heat. For example, the oxidation 

 of such foods as carbohydrates, fats, and proteins releases heat for use 

 by the living organism. 



A living organism which generates large quantities of heat through 

 its activities is frequently not very efficient. In such cases much more 

 heat is liberated than is required by that organism. A plant is much 

 more efficient in this respect than animals generally are. Most of the 

 heat acquired by plants is absorbed from the surroundings, and much of 

 it is lost by transpiration. So-called cold-blooded animals attempt to 

 maintain a body temperature somewhat similar to that of their environ- 

 ment, while warm-blooded animals generate and conserve their heat so 

 as to maintain a rather constant temperature throughout life, regardless 

 of the environment. Animals lose heat (1) by conducting it to other 

 objects, (2) by radiating it, (3) by losing it through their feces and 

 urine, (4) by the process of evaporation from the lungs and the sweat 

 glands of the skin. 



