237 



In discussing the séries, not much needs to be said about the 

 degree of acidity. I should only like to briefly consider what acid it 

 is, that causes the high bydrogen ion concentration, especially as 

 my results do not tally with those of earlier investigators. Benecke 

 States that Aspergillus niger produces oxalic acid, when nitrogen 

 is supplied in the form of an organic compound. If ammonia 

 salts are given however, only the NH; ion is assimilated, while 

 NO3 ion forms nitric acid, which prevents the formation of organic 

 acids. Wehmer confirms this statement and adds, that the acid does 

 not check the growth of the fungus, but checks the development 

 of conidia. After some time the acid should disappear, because the 

 basic substances, formed by the breaking down of proteids, com- 

 bine with it. We shall see that thèse two last assertions are only 

 partly true. 



Boas and Leberle traced the acidity from day to day and they 

 found the most development of acid when NH4NO3 was given. 

 They also fcund, that the acid did not decrease as was the case, 

 when organic nitrogen compounds were given. They accounted 

 for the decrease by assuming, that the fungus itself assimilated the 

 oxalic acid, which was first produced. 



The results of Elf ving agrée very well with the others. He also 

 finds citric acid besides oxalic acid. As however the nutritive value 

 of the former is very high, it is consumed much more rapidly than 

 the latter. 



It is a pity, that none of thèse investigators extended their in- 

 vestigations over more than ten or twelve days. They hâve a very 

 exaggerated idea of the influence of the acid on the fungus and they 

 think that the acid disappears sooner or later in ail cases. They 

 are strengthened in their erroneous belief by the fact that the 

 degree of acidity gradually sinks during the last few days of their 

 observations. If only they had proceeded with the experiments 

 for a few more days, they would hâve seen their mistake. This is 

 seen very clearly in ail my tables, where the P^ has been deter- 

 mined. Besides I hâve been unable to find even a trace of organic 

 acid, when NHjNOo was used as the nitrogenous foodmaterial. 



