462 Mr. E. C. Grey. The Decomposition of 



the manner in which formic acid is decomposed by the natural and artificially 

 selected varieties of intestinal bacilli it might be possible to gain information 

 concerning the mechanism of the change brought about in the organism by 

 growth on chloroacetate agar which leads to the selection of strains in some 

 cases unable to decompose formic acid and in other cases unable to produce 

 it to the same extent as the normal strains from which they have been 

 derived. 



It seemed also of importance to determine what use the decomposition of 

 formic acid might be to the organism. Pakes and Jollyman (1901) and 

 Harden (1901) have shown that B. coli communis is capable of decomposing a 

 considerable amount of sodium formate, and that if a small quantity of 

 glucose be added, the amount of hydrogen produced over and above that 

 which could be derived from the glucose added is far greater than the amount 

 produced in the absence of the sugar. 



The writer has employed an artificially selected strain of B. coli communis 

 obtained by the chloroacetate method ; this strain produced in three days no 

 gas from sodium formate peptone water, and only acid but no gas from 

 glucose peptone water, but produced from a mixture of the two sufficient 

 gas to fill the' Durham gas tube (length 45 mm.) in 24 hours. The non- 

 production of gas from sodium formate peptone water alone is due, not to 

 the inability of the organism to decompose formic acid, but to the inhibitory 

 action of the alkali due to the natural alkalinity of sodium formate ; for if 

 the sodium formate peptone water were acidified with sulphuric acid until 

 the solution imparted a pink colour to litmus, it was found that a small 

 quantity of gas was produced by growth of the artificially selected organism 

 therein for two or three days. 



Other sugars and polyhydric alcohols have been employed with similar 

 results, which are discussed under Table II. 



By a quantitative study of the decomposition by the bacillus in question 

 of a mixture of glucose and calcium formate, the writer has been able to 

 show that both the amount of glucose and that of formate decomposed is 

 increased (Table III), and there can be little doubt that the formate and 

 sugar are mutually helpful, in that the alkali produced by the decomposition 

 of the former and the acid produced from the latter by neutralising one 

 another maintain that approximately neutral condition of the medium which, 

 as has been proved, is most favourable for the action of the organism. 



