282 STATE BOARD OE AGRICULTURE. 



Five hundred c. cm. of fresh milk was placed in a liter flask to which was added 

 one per cent of trikresol. The flask was then mercury sealed and placed away for 

 twenty- live days. An analysis made of the gases confined over the milk resulted as 

 follows: 



Total amount of gas analyzed 19.6 c. cm. 



Carbon dioxide c. cm. per cent. 



Oxygen 3.6 c. cm. 18.37 " " 



Residual gas 16.0 c. cm. 81.63 " " 



Here again the oxygen is gradually diminishing but no carbon dioxide appears to 

 take its place as is the case with fermentation. The reason given for the failure of 

 carbon dioxide to appear in the case of lysol will not hold with the neutral trikresol. 



Milk to which lysol or trikresol has been added cannot be regarded as normal milk, 

 yet from this work there is indicated an absorption of oxygen ; carbon dioxide is not 

 found present, but should normal conditions be maintained there is a possibility of its 

 appearance. Furthermore what carbon dioxide exists in the milk as gas could with 

 difficulty be detected by an analysis of the confined air over the milk. 



XII. THE ACTION OF 100 PER CENT OF CARBON DIOXIDE UPON THE DEVELOP- 

 MENT OF BACTERIA. 



From the results of the foregoing work with the gas-content of milk we are now 

 led to a study of the influence of carbon dioxide upon micro-organisms, for it is a 

 general and an indefinite belief that aeration has a direct bearing upon the bacterial 

 life usually present in milk. Inasmuch as there is a high percentage of carbon dioxide 

 in milk, it is probable that its presence might have some effect upon the development 

 and increase of the bacteria found and thus change the course of possible milk fermenta- 

 tions. That carbon dioxide does exert an influence has been shown by Delbriick and 

 Foth (16), Hansen (17), Ortloff (18). The gist of the conclusions reached by the 

 experimental labors of these men, although not wholly in unison, is found in the 

 restraining effect which carbon dioxide has upon the multiplying power of the yeast 

 cell and upon its fermenting energy; also in its stimulating action upon the individual 

 fermenting capacity of the yeast cell apparently in its search for an oxygen supply. For 

 outward manifestations, there would appear only a restraint in fermentation develop- 

 ment. To arrive at a comprehensive understanding of the situation in its most direct 

 relation, carbon dioxide under varying conditions was employed to definitely ascertain 

 its influence upon micro-organisms. In the first trial carbon dioxide in its free state 

 was used to determine its direct bearing upon micro-organisms in plate cultures. 



To accomplish this, two sets of plates as nearly identical as possible were made of 

 the same micro-organisms; one set to be kept in the air and the other to be confined in 

 Novy's anaerobic plating apparatus into which carbon dioxide was passed until the 

 percentage reached one hundred. These plates were allowed to develop 48 hours or 

 until they were thought to be fully developed, when the plates from the anaetobic 

 apparatus were removed and both sets counted at the same time and closely compared. 

 In all of this work pains-taking care was exercised to observe the most careful technique 

 in securing exact conditions in every respect for the two sets of plate cultures studied — 

 a single batch of media, the same diluted fresh bouillon culture, the same loop for 

 measurement, the same environment during development excepting the factor, carbon 

 dioxide, — all were brought under the closest scrutiny. The carbon dioxide used was 

 generated from sodium carbonate and sulphuric acid. The results of these studies are 

 tabulated below: — 



(16.) Wochenschrift fur Brauerei, 18S7, p. 37. 



(17.) Cent. f. Bakt. Bd. I. 1887. 



(18.) Cent. f. Bakt. Bd. VI, S. G76, 721, 753. 



