The formation of proteids in plans-cells. 45 



can be utilised in higher concentration than sodium acetate, and 

 this in a higher one than acetic ester or phenol, the latter form- 

 ing in 0,08 % solution a meagre food for a micrococcus,^ although 

 in higher concentrations a poison for all kinds of bacteria. The 

 more easily a compound is attacked by the cells, the quicker the 

 development of new cells. 



As sources of carbon : alcohols, acids, ketons, aldehydes, 

 carbohydrates, esters and bases can serve. As sources of nitrogen : 

 nitrates, ammonium salts, amido-acids, ureas, guanidins, nitriles, 

 amines, ammonium bases can serve. As sources of sulfur may be 

 utilised not only sulfates but also organic sulfur compounds, as 

 sulfons, sulfonic acids and probably also sulfides (methyl sulfide). 

 Our observations in regard to the sources of carbon teach us : — 



1) The nutritive quality of acids is enhanced by the en- 

 trance of alcoholic hydroxyl-groups ; thus lactic acid is superior 

 to propionic acid. 



2) The nutritive value of alcohols is increased with the 

 number of the hydroxyl-groups : glycerin is better than propyl 

 alcohol. 



3) The presence of aldehyde-or keton-groups increases the 

 nutritive qualities : glucose is better than mannite ; acetyl acetic 

 ester is better than acetic ester. 2) 



4) The lower alcohols may be used in higher concentration 

 than the higher ones (amyl alcohol). 



5) The lower members of the fatty series are more easily 

 assimilated than the higher members ; sodium acetate being far 

 superior to sodium valerianate. 



6) The unsaturated ring systems are generally not favora- 

 ble ; for instance antipyrin and dimethyloxypyrimidin appear 

 to be entirely unsuitable and while benzoic and salicylic acid 

 are very poor sources of carbon, phenyl acetic acid, containing a 

 CH 2 group, is far better, and chinic acid, containing a saturated 

 benzol-ring with 4 CHOH groups is a very good source. 



To carry out such experiments, mineral solutions are 

 prepared containing 0,1 — 0,5% dipotassium phosphate, 0,01 — 

 0,05% magnesium sulfate and 0,1 — 0,2% potassium nitrate or 



1) Compare Niigeli, Ber. Bayr. Akad. d. Wiss. 1879. 



2) I have here operated with 0,1 o/ 0 solutions. Biol. C. 10, 585. 



