INTRODUCTORY 



In the historical part, we have seen that the animal organism 

 cannot live very long upon an artificially prepared diet. Since 

 systematic investigations into the vitamine requirements of all classes 

 of plants and animals have not yet been made, it is not possible to 

 say with entire certainty that the above contention is generally true. 

 The firmly established importance of the vitamines for the existence 

 of certain animals and plants, organisms which are far removed from 

 each other genetically, makes it apparent that these substances are 

 of universal importance to life. 



It is evident that there are differences in the qualitative and 

 quantitative requirements and it may later develop that various 

 organisms need various quantities as well as various kinds of vita- 

 mines. We shall briefly enumerate the facts that have led us to this 

 conclusion, and point out how many types of vitamines are known 

 up to the present. We choose to speak of vitamine types in this 

 case, and not of definite vitamines, for as long as these substances 

 remain unidentified, and till such time as they may be compared 

 with each other in the pure state, it is obviously impossible to talk 

 of their identity. Until now, we have differentiated three such 

 types. Whether with these three types we have finally reached 

 the possible limit, it cannot be stated definitely; however, it appears 

 unlikely that Nature, in the variety of its manifestations, essential 

 conditions and intensity of metabolism, should limit itself to only 

 three types. On the other hand, it is possible that after purification, 

 that which seemed to us a single substance might well prove to be 

 a mixture. We may be dealing with complex substances having 

 some chemical groups in common, and others, the significance of 

 which has not yet been demonstrated. 



It would be quite premature to propose, with McCollum (69), that 

 only two or three vitamines exist in nature. He arrived at this 

 conclusion as a result of his numerous rat experiments, which showed 

 that for this species two types of vitamines were sufficient, and 

 thereupon drew conclusions that were to be applied to the entire 

 plant and animal kingdom. Although we are very well informed as 

 to the food requirements of rats, compared to those of other organ- 



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