EXPERIMENT STATION BULLETINS. ,3S9 



no definite action could be noticed ' upon the bone or rock phosphate. 

 The solvent action of some germs seemed to be greater in the presence 

 of the larger percentage of sugar, while that of others seemed to be as 

 great with the 1% as with the 4%. 



In order to get the cultural conditions more nearly like ihose exist- 

 ing in the soil, we used a medium composed of soil leacliings with 

 2% agar. No solvent action could be noticed. But when sugar was 

 added to this medium, the action was about as marked as that with 

 the synthetic medium described above. 



Now, if we used meat infusion — one liter of water to 500 grams of 

 beef — instead of the water in the synthetic medium, we found that the 

 solvent action exerted by the bacteria was not nearly so great. 



It might be interesting to note here that according to our experiments 

 those germs which, in the presence of sugar, are the most active acid 

 l^roducers are also the germs which, in the presence of albuminoids and 

 tlie absence of sugar, are the most active alkali producers. And again 

 these active germs are the ones which have shown the greatest solvent 

 aclion. 



Thirty-six out of fifty different bacteria isolated from the soil were 

 found to give a definite, visible solvent action. One of these which produces 

 no gas from sugars, but a larger amount of acid than any of the others, 

 shoAvs the greatest action upon the calcium carbonate; while other 

 germs which produce gas, largely carl)on dioxide, but not as much acid 

 as the former, give an action more marked than that of the stronger 

 acid producers upon the di-calcium and tri-calcium phosphates. These 

 ])oints, with others noticed during the experiments, have led us to be- 

 lieve that, while acid is an important factor is dissolving insoluble 

 jthosphates, the carbon dioxide liberated fioni the carbohydrates by the 

 gas producing bacteria must not be overlooked as a solvent agent. 



This agar plate method for determining the solvent action of different 

 organisms, while only in a measure quantitative, has proven to be a 

 very useful one in our studies with calcium carbonate, di-calcium and 

 Iri-calcium phosphates. However, with the more complex forms of the 

 phosphate as met with in bone and phosphate rock, it has been unsatis- 

 factory and has been found to be not sufficiently delicate to warrant 

 our recommending it for general use with all insoluble compounds. The 

 scheme commends itself especially where it is desired to determine in 

 a rough way and in a short time the solvent action of a large number of 

 microorganisms upon different media containing the insoluble com- 

 pound in question. 



Table No. 15 shows the relative number of soil bacteria giving a 

 solvent action upon Ihe secondary and tertiary calcium phosphates and 

 calcium carbonate. The medium used was the synthetic agar containing 

 4% saccharose. As the results with the bone and the rock phosphate are 

 all negative, owing to the rough plate method emjiloyed in obtaining this 

 data, thev are omitted from the table. 



Legend for- Table 15: 



-f- means, detinil<' srdutioii. 

 ? means, suspected solution. 

 - iiu'ans. MO solntion uoticeablc. 



