1922] GREAVES—SOIL 175 
ciated with the ammonia. The carbonic acid would play an 
important part also in this reaction: 4H,.CO,+Ca,(PO,).= 
2 Ca(HCO,),.+CaH,(PO,).. They found that neither ammonifying 
bacteria nor nitrobacter liberated appreciable quantities of sol- 
uble phosphorus from insoluble phosphates. Whereas this would 
readily occur in soil poor in calcium carbonate, yet in those rich 
in calcium carbonate there would be only small quantities of 
phosphorus liberated. This is the conclusion reached by KELLEY, 
but where the soluble phosphorus is rapidly being removed by the 
growing plant, there is little doubt but that the various soil organ- 
isms play an important part in rendering phosphorus soluble. 
Moreover, it is quite evident that Azotobacter in their metabolism 
transform soluble inorganic soil constituents either into soluble or 
insoluble organic forms. This is especially true of phosphorus 
which is found in the ash of these organisms in such large quantities. 
The phosphorus, on the death of the organism, is returned to the 
soil in a readily available form, for StoKLasa has found that 50 
per cent of the nitrogen of these organisms is nitrified within six 
weeks, and there is no reason for believing that the phosphorus 
would be liberated more slowly. There is also the possibility that 
many of the constituents of the bacterial cell may become available 
through the action of autolytic enzymes without the intervention 
of other bacteria (19). 
It is further evident that an organism which possesses the 
power when growing under appropriate conditions of generating 
1.3 times its own body weight of carbon dioxide during twenty-four 
hours (34) must greatly change the composition of the media in 
which it is growing. Water charged with carbon dioxide is a 
universal solvent, and will attack even ordinary quartz rock. 
Granite and rocks related to it are rather quickly attacked with the 
liberation of potassium and other elements. Likewise, it would 
act upon the tricalcium phosphate of the soil with the formation 
of more readily soluble phosphates, for this substance is four 
times as soluble in water charged with carbon dioxide as it is in 
pure water: Ca,(PO,),+2CO,+2H,O =Ca.H.(PO,).+Ca(HCO;).. 
Moreover, the nitrogen-fixing organisms produce, among other 
products, formic, acetic, lactic, butyric, and other acids. The 
