Bacterial Test for Plant Food Accessories [Auximones). 107 



Accordingly, nitrifying solutions containing seventeen parts per million of 

 sucrose, maltose, asparagine, peptone, leucine, tyrosine, and hordein 

 respectively, were inoculated with the organisms, but no growth occurred 

 after four days. Fresh liquids, containing twenty, forty, and sixty parts 

 per million of each of these substances were then tested, with negative 

 results ; and not until the proportions had been increased to two hundred 

 parts per million in each case was any growth apparent. Even then the 

 characteristic scum was not obtained, the whole medium becoming uniformly 

 cloudy. This shows that the scum formation is due to the specific action 

 of auximones. 



The next step was to determine if the presence of the accessory substances 

 concerned with animal nutrition would induce scum formation. These 

 substances have been obtained from various seeds and yeast. For this 

 experiment the seeds employed were wheat, maize, and peas. They were 

 first soaked in water for 24 hours, then dried and left at room temperature 

 for two days, when their radicles were from J to 1 inch in length. They 

 were then ground up in a mortar, and a phosphotungstic fraction obtained of 

 these, of similar quantities of the dry seeds, and of yeast, in the same way as 

 described for bacterised peat. The extract of 1 grm. of each of the seeds and 

 of yeast was used for testing, and no scum could be obtained with the 

 phosphotungstic fraction of dry maize and dry peas. A fair scum, however, was 

 obtained in from two to three days with the fractions from yeast, germinated 

 wheat, peas, and maize, and a thin scum from dry wheat. In the case of 

 wheat, the seeds are invested with a pericarp, and it was from this region of 

 rice grains that an animal food accessory was first obtained. It is thus 

 evident that the scum-forming organisms are able to serve as a qualitative 

 test for food accessories in general. 



Having thus obtained an indicator for auximones, it becomes a compara- 

 tively simple matter to examine other materials for their presence. Since 

 bacterised peat, in which auximones are relatively abundant, is obtained by 

 bacterial action upon raw peat, it was decided to investigate other samples of 

 decomposing organic matter for these substances. Quantities of fresh stable 

 manure, and also of a well-rotted two-year-old manure, were procured and 

 fractionated in the usual manner. Portions of these fractions, corresponding 

 to 1, 2, 4, 6, 8, 10, 20, 40, and 50 grm. respectively, of both fresh and rotted 

 manures were added to nitrifying solutions, three flasks being used for the 

 investigation of each of the separate portions. After inoculation with the 

 scum-forming organism, the whole series of flasks was incubated for four days 

 when the first indication of a scum appeared in the liquids containing the 

 fraction from 10 grm. of rotted manure, and in those which had received the 



