262 STATE BOARD OF AGRICULTURE. 



the present we must content ourselves with the references to be gained from the 

 evidence at hand. The aerating methods now in vogue in dairy operations may or 

 may not yield results. It is not necessary to say whether these methods are effectual 

 or not; for our purpose their value cannot be determined until each method has been 

 worked out with pains-taking care. As soon as there has been established a non- 

 aerated milk and a satisfactory aerated milk, then we may hope to reach some definite 

 conclusion in its application to the dairy. Before this is done, the one hope that can 

 be held out is that some of the aerating methods now employed may be giving some 

 advantages over the non-aerating methods besides those which are recognized in the 

 removal of odors and taints in a slight degree. 



The work which follows has for its immediate aim the demonstration of what con- 

 stitutes non-aeration and aeration and how it may influence the condition of the milk 

 itself and the germ content of the milk. After getting into the work it has been found 

 necessary to eliminate for the present several side-problems which bear directly upon 

 aeration and confine ourselves to the main line planned at the start. It should be noted, 

 therefore, that all the aspects are not to be satisfactorily considered in this article, but 

 rather, that a path has been hewn out of an unknown forest of doubt and ignorance 

 which we may follow with profit in the future and may eventually be led to the 

 solution of the whole question. 



II. REVIEW OP THE GAS-CONTENT OP MILK. 



The first problem which confronts the experimenter is to obtain a knowledge of the 

 gas-content of the milk before exposure to the air. Dr. Felix Hoppe (9), in 1859, 

 made a study of the gases of milk from a goat. 



His analyses are as follows: — 



First Analysis. 



Carbon dioxide 9 parts. 



Oxygen 9.57 " 



Nitrogen 8.43 " 



This trial should be regarded in the nature of a preliminary test. 



In securing the milk he drew it into a funnel contiguous to the end of the teat of 

 the goat, and conducted the milk into a flask from which the air was expelled as the 

 milk filled the flask. To this method of securing the milk, there is an objection 

 because the milk had been exposed to the oxygen of the air, not only in its agitation 

 while passing along the tube in contact with the air, but also in the surface contact 

 with the oxygen in the air in the flask itself. 



Second Analysis. 



Carbon dioxide 55.15 per cent. 



Oxvgen 4.29 " 



Nitrogen 40.56 " " 



He secured 12.08 volumes of gas from 402 volumes of milk measured at 0° and 1 M 

 pressure. 



With this analysis the same criticism can be made as with the first analysis. He 

 used the funnel but improved the design of the flask. When these analyses are compared, 

 therefore, with the analyses of the gases from the milk immedia'tely after milking, it 

 will be seen at once that he has reached practically the same results; consequently his 

 analyses are no more than the analyses of gases from milk immediately after milking. 

 Without reference to his method of securing the gas, which is also open to condemna- 

 tion, it follows that this work may be disregarded and is no criterion to follow when 

 considering the gas-content of milk as it comes from the udder of the cow. 



Stechnow (10) adopted another method of securing the milk. Olive oil. the best 

 obtainable, was used to cover the milk. He inserted the end of the teat into the oil, 

 then milked, thus maintaining a layer of oil over the surface of the milk. This, doubt- 



(9.) Arch. f. path. Anat. und Physiol, u. f. klinisehe Medicin. 1850, Bd. 17. 5. 417. 

 (10.) Zeit. f. rat. Medicin von Henle u. rfeuffer, Bd. 10, S. 2S5. 1861. 



