182 METABOLISM 



4. Peptone Organisms. Scarcely any growth takes place with asparagin 

 or ammonia ; nor can proteid replace peptone. Examples : Bacillus anthracis^ 

 Bacillus proteus, lactic acid Bacteria (BEIJERINCK, 1901). 



5. Proteid Organisms. Micrococcus gonorrhoeae and Bacillus diptheriae 

 require proteid and are unable to live in peptone or other nitrogenous substrata. 

 They certainly exist in nature as parasites only and, strictly speaking, do not 

 belong to this category. 



6. Mention must also be made of organisms which use the free nitrogen of 

 the air in preference to other nitrogenous material. We shall refer to them 

 elsewhere. 



The types which have been indicated show that among Fungi and Bacteria 

 there are all sorts of transitional forms, from those which are able to assimilate 

 nitrogen just like autotrophic green plants to suchas are dependent on previously 

 elaborated proteid. We may if we choose, therefore, designate the nitrate and 

 ammonia organisms as autotrophic so far as their relation to nitrogen is concerned, 

 and term the others heterotrophic. But just as we found that the requirements 

 of the plant, re carbon, often depended on the combination in which nitrogen 

 was presented, so conversely the nitrogen requirements depend on the 

 source of carbon. Thus A. FISCHER (1897, p. 53) found that Bacillus coli, 

 Bacillus subtilis, and Bacillus pyocyanus could use nitrate in presence of glucose ; 

 but if glycerine were substituted for glucose, Bacillus pyocyanus alone thrived ; 

 the others used ammonia exclusively as a source of nitrogen when glycerine 

 formed the source of carbon. When proteid or peptone was supplied as nutri- 

 tive nitrogen, an additional supply of a special source of carbon was found to be 

 unnecessary ; frequently the same was found to be true of asparagin. A com- 

 parative research on the nitrogen requirements of different Fungi would be of 

 special value since the results hitherto obtained are exceedingly fragmentary, 

 and similar researches are needed on the nitrogen requirements both of omnivors 

 and of specialists. 



Nor are we able to answer comprehensively the problem as to the best 

 combinations of carbon and nitrogen, although it is generally held that a nutri- 

 tive solution containing peptone and glucose acts best. On the other hand, 

 CZAPEK (1902) has shown in the case of Aspergillus that the amino-acids are 

 preferable to peptone in presence of glucose. Taking into account the state- 

 ments in the literature, however, it cannot be said that any law of general 

 applicability has as yet been formulated. BEIJERINCK (1891) found, for 

 example, that peptone alone (as a source of carbon and nitrogen) was a better 

 medium for Bacillus cyaneofuscus than asparagin and glucose, and WENT (1901) 

 demonstrated in the case of Monilia that when glucose formed the source of 

 carbon, peptone was preferable to all other substances ; with asparagin it reached 

 only a third of the increase in weight gained when peptone was supplied, while 

 leucin was found to be far inferior to potassium nitrate. Ammonium salts of 

 acetic acid, tartaric acid, &c., were found to be specially unsuitable combina- 

 tions of carbon and nitrogen, although many Fungi for long maintained their 

 growth in them. 



The ubiquity of Fungi and of biologically related plants is due to their 

 capacity for living on the most varied organic materials, together with their 

 remarkable power of adapting themselves to highly concentrated nutritive 

 solutions. The general occurrence of dead vegetable tissues renders the exist- 

 ence of Fungi possible in most situations, and so we see that on dead leaves, twigs, 

 and fruits, a covering of Fungi soon appears, provided only the general condi- 

 tions be sufficiently moist. Dead animals also, as well as animal excrement, 

 form a suitable medium for the growth of Fungi, so long as the reaction be acid, 

 as is generally the case in plant debris ; when the reaction is alkaline, on the 

 other hand, Bacteria are the dominant organisms. Under the influence of 

 these microscopic forms a decomposition of the debris of the higher organ- 



