72 DYNAMICS OF LIVING MATTER 



all the constituents of living matter, e.g. fats, proteins, nucleins. 

 Raulin, a pupil of Pasteur, has investigated with unparalleled thor- 

 oughness the optimal nutritive solutions for a fungus, Aspergillus 

 niger. Raulin * determined which nutritive solution gave the great- 

 est development of living matter from a given quantity of spores, and 

 found that it possessed the following composition : 



Water 1500 g. 



Cane sugar 70 g. 



Tartaric acid 4 g. 



(NH 4 ) 3 PO 4 0.60 g. 



K 2 CO 3 ......... 0.60 g. 



MgCO 3 0.40 g. 



(NH 4 ) 2 SO 4 0.25 g. 



ZnSO 4 0.07 g. 



FeSO 4 ......... 0.07 g. 



K 2 SiO 3 ......... 0.07 g. 



Of course, to this list must be added atmospheric oxygen. 



Part of the free acid in Raulin's solution is neutralized by the HO- 

 ions due to the presence of (NH 4 ) 3 PO 4 and K 2 CO 3 in the solution. 

 The sugar, fatty acid, ammonia, SO 4 , and PO 4 are used for the build- 

 ing up of living matter ; but it is not clear what the role of K, Mg, Zn, and 

 Fe is. It is remarkable that Ca is not required, and it seems to be a 

 general fact that Ca is not of great importance for the fungi, while it 

 is of great importance for animals, and apparently also for the higher 

 plants. But what is the role of the cations? 



It has been noticed that the living tissues of plants, as well as of 

 animals, possess a selective power for certain salts, especially for K-salts. 

 Although in fresh-water streams the concentration of K-salts is often 

 very low, the plants which live in it are capable of storing up a com- 

 paratively large amount in their tissues. The muscle of animals shows 

 the same phenomenon, inasmuch as it contains a much higher per- 

 centage of potassium than the blood. This "selective power" admits 

 of only one explanation; namely, that the potassium is used for the 

 building up of more complex compounds in which the K cannot be 

 dissociated as a free ion. If a tissue utilizes one kind of metals in this 

 way, e.g. K, while another metal, e.g. Na, is chiefly used for the forma- 

 tion of dissociable compounds with Na as a free ion, the consequence 

 will be that the ashes of a tissue contain K and Na in altogether differ- 

 ent proportions from what they are contained in the surrounding solu- 



* See Duclaux, Traite de microbiologie, Vol. I, p. 176, li 



