44 THE FORMATION OF PROTEIDS IN PLANT-CELLS. 



tions or in fermentations. We leave in this chapter, however, 

 the fermentative activity out of consideration, and mainly treat 

 of the protein formation and nourishment of the aerobic microbes 

 and mould-fungi: — We observe here that a great number of 

 organic compounds of different chemical constitution may serve 

 for nourishment and development. There can be hardly any 

 doubt but that in all these different cases the same proteids 

 result, otherwise the structure and the functions of the pro- 

 toplasm formed would show variations, new species would spring 

 into existence with ease, according to difference in food. We 

 find however the same species of a bacterium 1 ' or of a mould- 

 fungus, whether we nourish them once with peptone, or with 

 sodium tartrate as a source of carbon, whether we offer glycerin, 

 glucose or laevulose, xylose or arabinose, glycol or chinic acid. 

 It makes no difference in the resulting species, whether we offer 

 once nitrates, the next time leucin or a third time betaln as 

 a source of nitrogen. 



This circumstance teaches us not only that the proteids 

 and protoplasms formed from different food, remain in one 

 species the same, but also that the formation of proteids must 

 commence with relatively simple atomic groups, that are prepared from 

 the most different kinds of substances by oxidation and decomposi- 

 tion.^ 



Certain combinations are excellent nutrients, like peptones, 

 others poor ones, like valerianic acid, others again do not serve 

 at all as sources of carbon, as oxalates or pyridin salts, and others 

 are poisons, as phenylhydrazin. Small chemical changes may 

 convert a nutritive compound into a poison and the poison again 

 into an indifferent body. These qualities depend upon the chemi- 

 cal constitution and are to some extent merely relative concep- 

 tions determined by the degree of concentration. Glucose 



1) The characters of bacteria may however be modified by changing the condi- 

 tions of cultivation; but whether such modifications would lead in course of time to 

 new species, which would be of high importance in connection with the problem of 

 evolution, remains to be investigated. 



2) Pasteur was the first, who recognised the capability of mould-fungi and bacteria 

 to grow in solutions free from protein compounds, i. e. to form protein and protoplasm 

 from simply constituted combinations, as tartaric acid, ammonia and sulfates. Up 

 to that time (1858) the opinion prevailed that fungi, like animals, could only subsist 

 upon proteids. 



