EXPERIMENT STATION BULLETINS. 301 



gases per se, but the fact that such a striking change is taking place is of sufficient 

 weight to assist in the solution of pertinent problems. 



We have not positively shown that these gases which have been subjected to study 

 are in loose combination or free but since the carbon dioxide runs down rapidly to a 

 certain percentage where its liberation from the milk becomes quite difficult and since 

 the percentage of oxygen may be increased above the content of air, there does seem to 

 be some evidence favoring the idea that there is a combination rather than the 

 existence of the gases in the free condition, yet small amounts of carbon dioxide are 

 with difficulty removed from distilled water and when such salts as sodium carbonate, 

 sodium hydrogen phosphate et cetera are in solution this difficulty is greatly increased. 

 Furthermore, when an attempt is made to simulate the effects of carbon dioxide in 

 milk by the use of free carbon dioxide there exists a marked similarity so far as the 

 growth of the germs is concerned, but just as soon as we begin to study the acid effects 

 upon the indicator we find that the carbon dioxide which we obtain does not act the same 

 as the carbon dioxide as we add it in the free state. However, it should be remembered 

 that the solubility of carbon dioxide in water is practically 100 per cent while the most 

 obtained from milk is not above 10 per cent by volume. It would be unsafe, therefore, 

 to draw a positive conclusion from the facts we have regarding the condition of carbon 

 dioxide in milk or the condition of oxygen; our knowledge must remain as it is. 

 The weight of evidence does not favor an apparently loose combination, because it may 

 be accounted for by the solubility of the gas, and thus must at first follow a rapid 

 reduction of carbon dioxide in the milk when exposed in an effort to establish an 

 equilibrium. 



The increase of oxygen during the milking process also must have considerable 

 influence upon our judgment relative to the common methods of handling milk in the 

 stable. If carbon dioxide is eliminated so rapidly and oxygen increases, there must 

 of course be a rapid interchange of gases going on during the milking process while 

 the milk is more or less agitated by the passage of the streams of milk from the teats 

 of the cow to the surface of the milk in the pail, and to the impinging of the streams 

 against the surface of the milk in the pail causing a churning effect. Now if this 

 interchange takes place as is indicated by the analyses over and over again, it follows 

 that if any obnoxious gases exist in the stable they must necessarily invade the milk 

 as does the oxygen ; by this means the milk is rendered unwholesome to a greater 

 or less degree by the gases existing in the stable. Should the operations which are 

 commonly in vogue at the present time be carried out and the milk disturbed by pouring 

 it through a strainer into a milk can or even over an aerator or cooler in the stable 

 air it is easy to understand how the gases of the milk and the gases of the air find an 

 equilibrium. This of course means that the gases in the milk and the gases of the air 

 must substitute each other to a great extent. The practice of milking in filthy stables 

 containing filthy odors is therefore reprehensible. 



There may be an elimination of taints which originated by means of physiological 

 processes in the cow or emanate from bacterial fermentation processes. It has been an 

 old and common belief and is still that animal odors and taints are to a large extent 

 removed by aeration. This is evidently true. In our experience we have so removed 

 the animal odor from the milk that no odors were perceptible even Avhen warmed. 

 Knowing that the gas-content of milk and the air gases interchange freely when milk 

 is agitated or spread out in a very thin film the explanation of this removal of animal 

 odors and taints appeals to our understanding, and very naturally, in the light of 

 preceding studies. However, the methods employed for aeration must be effective to 

 accomplish satisfactory results. 



The interchange of gases going on in a closed can of milk over which is a small air 

 space as is usually the case should be looked upon as resulting from fermentation 

 processes rather than from physical or chemical interchange of gases. Blyth has 

 satisfactorily shown that milk undergoing fermentation soon reaches the point where 

 oxygen completely disappears and carbon dioxide is practically the only gas present. 

 In connection with antiseptics in fresh milk where all fermentation has been arrested 

 it is true the oxygen greatly diminishes in amount, but it requires some time to bring 

 about a marked diminution of this gas, consequently the interchange of gases is due 

 to a slow oxidation process such as is well known to exist in a great many complex 

 organic compounds ; what oxygen may be present in the milk itself may be utilized by 

 numerous possible bacterial changes. It is apparently true that if milk remains 

 quiet that the oxidation which takes place through contact with the oxygen in the 

 milk is probably as slow as is known to be the case where oxygen permeates agar or 

 gelatine and influences the life zones of the media. We should not expect that where 



