276 CAROTINOIDS AND RELATED PIGMENTS 



made indicating that the yellow skin secretions of Jersey and Guernsey 

 cattle change their appearance with advance in the lactation period. It 

 is perhaps not too hazardous to predict that it is only along such lines 

 that a correlation may be expected to exist between skin pigmentation 

 and butter fat production for cows of the Channel Island breeds. As 

 a matter of fact Hooper's data show a slight indication of such a cor- 

 relation for one group of cows but not for the other whose records and 

 skin colorings are recorded. An investigation of the theory from the 

 point of view of a fading of the skin color during heavy production 

 might lead to very profitable results. 



This brief discussion indicates the practical ends which may be 

 served through the occurrence of plant carotinoids in the animal body. 

 The whole subject is a fascinating one and offers as many unsolved 

 problems as any other phase of experimental biology and biochemistry. 

 The writer can not conclude this monograph, however, without inviting 

 the attention of the biochemists to this field of work. The extension 

 of the frontiers of our knowledge regarding these pigments which are 

 so abundantly distributed in so many plants and animals is certain to 

 prove a profitable as well as an interesting undertaking. Who can 

 predict the magnitude of importance of the discovery which lies just 

 beyond the horizon in this or any other expedition in the search after 

 truth? 



Summary 



The functions of the carotinoids in plant tissues have not been defi- 

 nitely determined. The various theories which have been advanced 

 include the following: 



(1) Carotin plays a role in plants similar to that of the hemoglobin 

 of the blood ( Arnaud) . 



(2) Carotin acts as a reserve substance (Zopf, Kohl) . 



(3) Carotin shares in the work of C0 2 assimilation by acting in- 

 directly as a catalyst for the decomposition of atmospheric C0 2 

 through its absorption of light energy which it helps to transform into 

 heat (Kohl). 



(4) Carotinoids protect cell enzymes against the light rays which 

 they absorb (Went, Kohl). 



(5) Carotin in flowers and fruits acts biologically as a lure for 

 insects, birds and other animals, in connection with the spreading of 

 pollen and seeds (Kohl). 



