190 MICHIGAN ACADEMY OF SCIENCE. 



must therefore enter the milk, thus accounting for the stable gases in 

 the milk. On the other hand, after the milk is quiet in the vessel what 

 interchange takes place is very slow. It follows that any agitation of 

 the milk in the stable enables the gases arising from the "excrements of 

 the animals and fermentation to mix with the milk. Such agitation is 

 milking, pouring milk from a pail to a milk can or straining the milk in 

 the stable. The pure outdoor air is indicated as the best environment for 

 milking purposes to overcome odors and taints. We also find, if un- 

 sterilized milk is confined with air, that all of the oxygen is absorbed and 

 carbon-dioxide given off. This absorption and elimination is not in the 

 same proportion. In sterilized milk this is not true. The oxygen remains 

 constant and no carbon-dioxide forms. From this it would seem that the 

 cause of the absorption of oxygen and the elimination of carbon-dioxide 

 is a fermentation induced by micro-organisms. This is proved by ex- 

 periments with specific micro-organisms in pure culture in sterilized 

 milk. Nearly all of them absorb oxygen and give off carbon-dioxide. 

 Occasionally, however, there is one which, apparently, does not apprecia- 

 bly eliminate carbon-dioxide and consume oxygen. However, when lysol 

 or tricresol is added to milk some oxygen disappears but no carbon- 

 dioxide gas is eliminated. 



So far as micro-organisms may be determined, there is nothing other 

 than an indirect bearing which, however, is of considerable weight, for 

 the character of the fermentation in milk may be the direct cause for 

 good or evil effects when the milk is consumed. 



When micro-organisms are subjected to an atmosphere of carbon-dioxide 

 there is found a variable influence. Usually the micro-organisms are re- 

 tarded in their development, some succumb completely, even when the 

 percentage is as low as forty. This is also true of hydrogen but not so 

 true of air minus its oxygen through its absorption with alkaline pyro- 

 gallol. If the carbon-dioxide exists as free carbon-dioxide in the milk 

 or even in loose combination, in which light I am more likely to regard 

 it, Ave should expect to find that unexposed milk would have a detri- 

 mental effect upon the growth of micro-organisms as compared with 

 aerobic conditions. This appears to be the case, for when the same milk 

 is placed under anaerobic and aerobic conditions, the aerobic milk will 

 produce much larger numbers of bacteria usually than the anaerobic milk. 

 This is not due to any germicidal action the milk may have, for this prop- 

 erty is practically the same under both conditions ; it is further not due to 

 an increased amount of acidity on the part of the anaerobic conditions, 

 for the aerobic milk, after the beginning of an increased acidity 

 soon outstrips the anaerobic milk. It is true that the acidity of milk ex- 

 posed to the air at first drops when measured by phenol-phthalein while 

 that under anaerobic conditions does not. I explain this through the 

 influence of carbon-dioxide upon the phenol-phthalein, which was used 

 as an indicator, since I have been able to raise milk from 10° acidity to 

 37° acidity to phenol-phthalein simply by placing the milk in an atmos- 

 phere of carbon-dioxide for 24 hours. Since all my tests to show a direct 

 germicidal action from aeration have been negative, I am convinced that 

 the whole question lies in the possible character of the fermentation re- 

 sulting from the two sets of conditions. This of course opens a line of 

 work which is already pretty well known to us, inasmuch as it depends 

 upon the weighing of evidence as to whether anaerobic changes are more 

 likely to result detrimentally than aerobic changes. So far as the re- 



