PROPERTIES OF GROWTH SUBSTANCES 49 



chloroform and twice from water. These crystals had a constant 

 melting point of 165°C. and showed the same strength in AE per 

 milligram as the first. 



Yeast, a Source of Heteroauxin. — Kogl and Kostermans 

 (1934, Mitt. XIII) have isolated partially pure heteroauxin from 

 cultures of yeast, after plasmolysis by ammonium chloride. The 

 melting point of the preparation was 163. 5°C., and its molecular 

 weight 193. Its physiological effectiveness amounted to 17,600,- 

 000 AE per milligram. Further purification might be expected 

 to bring it still closer to the characteristics of 3-indole acetic acid, 

 both in melting point and in physiological effectiveness. Similar 

 preparations of heteroauxin from Rhizopus and Aspergillus showed 

 molecular weights of 176 and 169, respectively, in good agreement 

 with the molecular weight of 175 for 3-indole acetic acid. 



The method employed by Kogl and Kostermans in the prepara- 

 tion of the growth substance from yeast was as follows : 



(1) One kilogram finely crushed yeast was mixed with 100 g. 

 pulverized ammonium chloride and allowed to stand for 24 hours. 

 This gave a viscous mass, which was acidified with hydrochloric 

 acid and extracted directly with a large quantity of ether, since 

 it was found difficult to filter or centrifuge it without great losses. 

 Two and one-half liters of peroxide-free- ether per kilogram of 

 yeast were used for the ether extraction ; in this step, shaking is 

 done with care in order to avoid the formation of inseparable 

 emulsions. In this way, a total of 50 kg. of baker's yeast was 

 plasmolyzed with ammonium chloride and extracted with ether. 



(2) The ether extract was evaporated down to 5 liters and shaken 

 up with 5 per cent bicarbonate solution. After evaporation of 

 the ether, a syrup with an unpleasant fatty-acid odor remained. 



(3) For the purpose of removing the lower fatty acids, the 

 mixture was heated in a vacuum to 100°C. (water-bath tem- 

 perature). There remained a residue of 6.5 g. with an effective- 

 ness of 120,000 AE per milligram. A small sample of this 

 material mixed with ferric-chloride-hydrochloric acid gave the 

 red color reaction for 3-indole acetic acid; after each of the 

 further steps, this color reaction was used to indicate whether 

 or not the greater amount of growth substance was still con- 

 tained in the expected fraction. (4) The active syrup was 

 boiled three times with benzene; the insoluble residue was then 

 3.5 g., with an effectiveness of 250,000 AE per milligram. (5) 



