66 University of California Publications in Agricultural Sciences [Vol. 3 



value to the zymologist, it is of considerable scientific interest. It is 

 with this thought that these experiments have been carried out in the 

 Laboratory of Zymology.* 



The salts tested in these experiments were the chlorides of potas- 

 sium, magnesium, calcium and sodium, each being taken up separately. 

 The reason for choosing these chlorides was that their metallic ions 

 (cations) are those most abundant in the ash of grape juice. Besides, 

 Loeb 1 and Lipman 11 have shown that the positive ions of these salts 

 have the most effect, while their negative ions (anions) have the least. 

 Owing to the fact that the effect of the chlorine ion is uniform in 

 all cases, the metallic ions show their characteristic effects on the yeast 

 culture very clearly. 



Choice of Solution. — It has been shown by Loeb with marine ani- 

 mals (Fundulus) , by Osterhout with higher plants (wheat), and by 

 Lipman with soil bacteria (Bacillus subtilis) that, for the growth of 

 living organisms, a nutrient solution must be physiologically balanced. 

 In order to grow the yeast in a medium whose constituents were 

 known both in quality and quantity, it was necessary to prepare 

 a nutrient solution from pure materials. Such a solution must con- 

 tain an adequate amount of nitrogen and phosphorus in order that 

 the yeast may grow rapidly. For this purpose a number of sub- 

 stances were tried, such as Witte's peptone, asparagin, urea, and 

 ammonium phosphate, in different concentrations, with pure cane 

 sugar or pure dextrose. Witte's peptone proved to be impure, being 

 very high in ash, and the others did not give satisfactory results. 

 As dextrose is not easily available in the market at present, pure cane 

 sugar had to be used as a carbohydrate food and as a source of fer- 

 mentable material. 



Later a synthetic solution was made with hydrolized pure cane 

 sugar, phosphoric acid, and ammonia, which was suitable for the 

 growth of yeast for experimental purposes. Although this synthetic 

 solution produces a slower rate of growth than grape juice, which is 

 a perfect physiologically balanced solution for yeast fermentation, it 

 gives sufficient growth for experimental work. To make it, a 50 per 

 cent pure cane sugar syrup was made with distilled water and a 

 measured amount (1 gram per 100 c.c. of syrup) of phosphoric acid 

 added. This syrup was hydrolized by boiling for one-half hour on 

 a slow fire, and was then neutralized with dilute ammonium hydroxide. 

 Litmus solution was used to test the neutrality of the syrup. The 



* These experiments Were carried out under the general supervision of William 

 V. Crucss. 



