New York Agricultural Experiment Station. i8i 



only lactic acid but also certain by-products, among wliich is 

 carbon dioxide. The milk-sugar is undergoing decomposition 

 all through the normal process of cheese-making, and the carbon 

 dioxide thus formed becomes incorporated in the cheese-curd to 

 some extent. In our normal cheese, the milk-sugar actually 

 present before the cheese was placed under the bell-jar amounted 

 to 0.3 per ct. of the cheese. This was changed into lactic acid 

 with the accompanying formation of carbon dioxide in the early 

 period of ripening and the carbon dioxide thus formed, together 

 with that occluded in the cheese mass, can readily account for 

 the relatively large amount of carbon dioxide found during the 

 first week in the normal cheese. In the case of the chloroformed 

 cheese, a certain amount of the milk-sugar had undergone fer- 

 mentation before chloroform was added, as shown by a deter- 

 mination of the sugar in the curd the day after the cheese was 

 made. The amount found was low compared with the amount 

 present in perfectly fresh curd. Such fermentation would pro- 

 duce small amounts of carbon dioxide, which would be absorbed 

 by the milk and pass into the cheese mass. Carbon dioxide thus 

 enclosed in a cheese would again be given out into an atmos- 

 phere such as was present in the bell-jar, that is, one free from 

 carbon dioxide. 



(3) Respiration of liz'iiig cells present in cheese as a source 

 of carbon dioxide. — It is well known that living cells give ot¥ 

 carbon dioxide as the result of respiration processes. It is also 

 known that in a fresh normal cheese of the cheddar type the 

 number of micro-organisms, generally lactic acid formers, in- 

 creases rapidly for about 10 days and then after about 25 days falls 

 very rapidly for a period of 10 days to a relatively small number, 

 as shown by Russell and Weinzirl.^*' In any case, we can not 

 look to the respiration processes of living cells in cheese as the 

 source of the carbon dioxide formed after the first few weeks. 

 As regards this possible source of carbon dioxide during the 

 early age of a cheese, when the micro-organisms are present in 

 enormous numbers, we should be justified in expecting that at 

 this time the amount of carbon dioxide produced would be very 



lONinteenth Ann. Rept, Wis. Exp. Sta., p. 95 (1896). 



