8 PREFACE 



which have been identified as carotinoids, are in reality merely derived 

 from the food. The assumption therefore seems justified that a similar 

 biological relationship exists between all the chromolipoids of plant 

 and animal life; in other words, that all animal chromolipoids are 

 derived pigments and are either true or modified carotinoids. 



The writer has had three main ideas in mind in preparing this mono- 

 graph. First, he has attempted to compile a thorough history of the 

 development of the chemistry of the plant and animal chromolipoids. 

 This has not been attempted before in this particular field. Second, 

 he has tried to present such information regarding the pigments as 

 would be useful to workers who desire to attack the many interesting 

 problems in this branch of plant and animal chromatology. Third, he 

 has made an effort to point out lines of research which might prove 

 attractive to those interested in this subject. The author hopes that 

 he has had a reasonable measure of success in his efforts. 



For the convenience of readers who have not been trained in sys- 

 tematic nomenclature the scientific name of the individual species of 

 plants and animals in which carotinoids occur has been supplemented 

 wherever possible by the common name. For the plants, this informa- 

 tion has been drawn largely from Bailey's Cyclopedia of Horticulture. 



It may be of interest to the reader to know that the carotinoid pig- 

 ments in plants and animals have proved to be of some practical 

 importance. The uses to which their occurrence in animals have been 

 put are reserved for discussion in Chapter XI of the monograph. The 

 occurrence of carotinoids in plants, particularly green plants, formed 

 the basis for the construction of the light filters used by the American 

 Army during the late \var for the detection of camouflaged foliage. 

 Natural green foliage reflects both green and red light, due to the fact 

 that the chlorophylls and carotinoids are present together in the chloro- 

 plastids. The visibility of the rays reflected from the carotinoids is 

 so low in the presence of the chlorophylls which are present in five to 

 six times the concentration of the orange and red pigments, that green 

 color only appears to be reflected. However, it was found possible to 

 construct a light filter which absorbed practically all light rays except 

 a wide band in the red at about 700|i|i, and a narrow band, with low 

 transmission in the green at about 500|4i, so that natural green foliage 

 viewed through this filter appeared red, while camouflaged foliage on 

 which green paint only was used, appeared green. 



The writer has encountered so much difference of opinion regarding 

 the correct pronunciation of certain words which are used very fre- 



