A STUDY OF SOME FACTORS IN THE CHEMICAL STIMULA- 
TION OF THE GROWTH OF ASPERGILLUS NIGER 
Robert Aaron Steinberg 
The distinction between ''nutrients" and ''stimulants" has been the 
subject of intensive study since synthetic culture media of known composi- 
tion have come into use. It was early observed that substances which 
were considered to be by no means essential constituents of protoplasm 
might still produce a marked increase of growth. The phenomena of so- 
called "chemical stimulation" due to the addition to a nutrient solution 
of substances not regarded as essential for growth are apparently of general 
occurrence. Such phenomena have been described for bacteria (i6), fungi 
(57) > algae (49), and the higher plants (25, 7, 33). These studies for the 
most part had for their aim to ascertain the effect of the substance in ques- 
tion on the growth and on respiration. I have reported elsewhere (64) 
on evidence that substances may be dissolved in sufficient quantity from 
the glass of the cultural flasks to cause a partial or even a maximum accelera- 
tion of growth. I have also presented evidence that the amount of growth 
as well as the concentration of "stimulant" necessary for its production 
varies with the strain of Aspergillus niger used (65). I shall report here 
on further experiments testing the significance of the degree of acidity of 
the culture medium and the effect of varying its iron or zinc content singly 
or together. These results are obtained by the use of a method of purifying 
the culture medium not hitherto used in such physiological experiments. 
Lastly I have attempted to correlate the facts in the literature of "chemical 
stimulation" with some of the newer data on the problems of nutrition and 
growth obtained by other methods. 
The studies of Pasteur (51) on the alcoholic fermentation of yeast led 
to extensive investigations of the food requirements of the fungi. It was 
determined by Pasteur in the course of his investigations that yeast could 
grow in an aqueous sugar solution containing ammonium tartrate and yeast 
ash. Beyond ascertaining that the yeast ashes could not be replaced by 
magnesium phosphate and a few other salts, the matter was dropped. No 
attempt was made systematically to investigate the elements known by 
him to be present, from Mitscherlich's (38) analyses, in the yeast ash. The 
analyses referred to are shown on the following page. 
The continuation by Raulin (54), a student of Pasteur, of these studies 
on the components of the yeast ash in relation to the growth of another 
fungus, " Ascophora nigrans" (Aspergillus niger), soon followed. Raulin 
330 
