53 PHYSIOLOGY OF NUTRITION. 



II. THE PRODUCTION OF PROTEIDS IN PLANTS. 



18. The Nitrogenous Food of Lower Organisms. 



It is very important to prove that the cells of many plants have 

 the power of producing nitrogenous organic bodies, e.g. proteids, 

 from non-nitrogenous organic substances (e.g. sugar) and nitro- 

 genous inorganic material. We experiment with yeast (Saccharo- 

 myces cerevisiee). 1 



We take three flasks, a, 6, c, of about 200 c.c. capacity. In a we 

 place 100 c.c. of distilled water, in 6 100 c.c. of Pasteur's food 

 solution (1,000 parts by weight of this solution consist of 838 

 parts of water, 150 parts of grape-sugar, or sugar candy [in my 

 experiments I mostly used the latter, since it is more readily ob- 

 tained pure than grape-sugar], 10 parts of Ammonium tartrate, 

 O2 parts of Magnesium sulphate, 0'2 parts of Calcium phosphate, 

 and 2 parts of acid Potassium phosphate) * ; in c 100 c.c. of a 

 fluid having the same composition as Pasteur's solution, except 

 that it contains no Ammonium tartrate. After plugging the 

 mouths of the flasks with cotton wool, we boil the three fluids for 

 some time, in order to sterilise them as completely as possible, 

 and after allowing to cool remove the plugs for an instant, and 

 introduce a small quantity of yeast into the fluids. We use 1 or 

 2 c.c. of yeast-containing fluid (see Appendix). The vessels, 

 closed with cotton wool, are exposed to a temperature of about 

 25 C. and put aside either in darkness or in the light, but fre- 

 quently agitated. The fluid in b rapidly becomes very turbid, 

 and very many new yeast cells are produced, which settle in a 

 mass at the bottom. The fluids in a and c either do not be- 

 come turbid at all, or very slightly. Since it is very difficult to 

 free yeast of all foreign substances, multiplication may possibly 

 go on to a very slight extent in a and c, but at all events the 

 copious multiplication which takes place in b (as may be more 

 exactly determined by filtering and then drying and weighing the 

 yeast obtained) shows that here alone are the normal life condi- 

 tions of the fungus fulfilled. The formation of new cells would 

 necessitate the elaboration of nitrogenous organic substances, 



* According to the researches of Molisch, fungi also require for normal de- 

 velopment to be supplied with iron. Generally sugar contains a certain quantity 

 of iron. To make quite sure, however, we may add to the Pasteur's solution 

 O'Ol per cent, of Ferric sulphate. 



