ADAPTATION 201 



glucoses instead of carbonic acid, as those products are 

 normal steps in their assimilation ; and it may also be fairly 

 easily understood that nitrogen can be offered in organic 

 form instead of as a nitrate. 



It was in the group of fungi that really important 

 adaptations with regard to the proper form - producing 

 alimentation were first discovered, and these are of a very 

 complicated kind indeed. Fungi are known to be satisfied 

 with one single organic compound instead of the group of 

 three fat, carbohydrate and albumen necessary for animals. 

 Xow Pfeffer showed that the most different and indeed very 

 abnormal compounds were able to bring his subjects to 

 a perfect growth and morphogenesis ; and, moreover, he 

 found that, if several kinds of such food were offered 

 together, they were consumed quite indifferently as to their 

 chemical constitution, but only with regard to their nutritive 

 value : that sort of food which had produced a better 

 growth than another when both were offered separately was 

 found to save the latter from consumption whenever both 

 were offered together. 



Here we are faced by one of the most typical cases of 

 regulations in metabolic physiology : the organism is able 

 to decompose compounds of the most different constitution, 

 which have never been offered to it before ; but never- 

 theless, it must remain an open question whether real 

 " secondary ' regulation has occurred, as nothing is known 

 in detail about the single steps of metabolism in these fungi. 

 There might be some ferments equally able to destroy different 

 classes of compounds, 1 and that the most nutritive compound 



1 In all cases where fungi of the same species are able to live on different 

 hosts, that is, to penetrate membranes of a different chemical character, a 



