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 2 ) 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 lævulose, 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 betaïn 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. 
