FUNCTI<>\ OF < AROTINOIDS I \ PLANTS, ANIMALS 2G7 



the pigment \vas found to lie independent of light, but dependent upon 

 oxygen. The fruits failed to redden in all cases of oxygen exclusion 

 even at a favorable temperature, but assumed a greenish yellow, yellow 

 or yellow-orange color with an accompanying loss of chlorophyll. 

 "\Yhether the latter colors were due to a formation of carotin and xan- 

 thophyll in the atmospheres of hydrogen and nitrogen employed, or 

 whether the carotinoids were merely revealed by the destruction of the 

 chlorophyll is not clear. Observations were also made on the catalase 

 activity of the fruits as well as their titratable acidity under the con- 

 ditions of lycopin suppression, with the result that it was found that a 

 very low catalase activity and decreased acidity accompany the con- 

 ditions which suppress the formation of the pigment. It is apparent, 

 however, that these are not the only factors concerned. 



Possible Function in Animals 



A quarter of a century ago the majority of the biologists accepted 

 the idea that all the visible pigments of animals, including the lipo- 

 chromes, are essential products of the animal metabolism. The pre- 

 vailing theories of evolution looked upon animal colorations as factors 

 in the existence of the species which had persisted solely for some 

 useful purpose. The theories which described the function of the 

 pigments in various terms, such as Protective Coloration, Warning 

 Coloration, Mimicry, Sexual Attraction, etc., all had their followers. 

 It is not our purpose to discuss these theories. One can find them 

 both adequately defended and impartially criticized in the treatises 

 current during the closing years of the past century. Suffice it to say 

 that, the writer does not possess a biological viewpoint which is suffi- 

 ciently developed along academic lines to appreciate "function" as an 

 abstract attribute of living organisms. Function, to be real, according 

 to his conception, must be concrete or physiological. Perhaps there 

 are those who will regard this as going from one extreme to the other. 

 If so, the explanation lies in the fact that this monograph deals only 

 with animal pigments which are derived from the food. Such pig- 

 ments, if possessing a function, must be linked with the physiological, 

 in this case the nutritional or metabolic processes of the body. 



We have seen in Chapter VII that great variation exists among dif- 

 ferent species of mammals with respect to their ability to absorb the 

 carotinoids from their food and deposit the pigments in their tissues, 

 or, if one prefers the opposite point of view, to destroy the carotinoids 



