EXPERIMENT STATION BULLETINS. 267 



Here is found considerable variation in acidity and, when these same milks 

 were employed for the cultivation of micro-organisms, it was also discovered 

 that micro-organisms responded differently to these different lots of milk. 

 Whether this response may be attributed to the acidity is not positively demon- 

 strated, for we know from past knowledge that the constituents of milk vary 

 widely; that is, the fat is subject to great variation as well as the casein of 

 milk. There may be some relation existing between the acidity and the normal 

 constituents of milk and instead of finding that the micro-organisms respond to 

 the degree of acidity, it may rather be found that they respond to the amounts 

 of different constituents present. Besides finding that the germs respond differ- 

 ently to milks from different cows, it was also found that milks gave different 

 results upon the addition of rennet; that is, the milks from different cows curded 

 upon the addition of identical amounts of rennet in dilferent periods of time. 

 We may conclude tentatively, therefore, from our studies of different milks, 

 that the results secured from the cultivation of germs in these different milks 

 are subject to as great variations as the results of chemical analysis. Bearing 

 this in mind, in order to secure satisfactory results in a study of associations 

 of germs in milk, it is necessary to restrict oneself to milk from the same source 

 and treated in an identical manner, otherwise unreliable data will be obtained. 

 It has been found necessary to introduce this brief survey of milk variation in 

 order to satisfactorily interpret our studies in association. 



When germ B, or the germ which we have employed in connection with the 

 lactic bacteria, has grown in milk for different periods of time, certain definite 

 changes are produced. Inasmuch as these changes give rise to the products 

 which we have shown may influence the growth of lactic bacteria as much as 

 living germs themselves, it is interesting to know what this breaking down or 

 digesting of'the milk may be. Studied from the chemical standpoint, we shall 

 find that the casein or cheese substance of the milk is almost completely dis- 

 solved and in its place are simpler nitrogenous products, such as peptones, 

 amido and ammonia compounds, as well as other products of more or less com- 

 plete digestion. It is impossible, from our present data, to definitely point out 

 which of these products favorably hastens the growth of lactic bacteria. It may 

 not be a single one, but several combined. At any rate, the digestion is doubtless 

 the means of furnishing such products as will hasten the growth of lactic bacteria. 

 It must be understood, too, that the products resulting from these particular 

 germs are not identical with the products of all germs of this class, for we find 

 germs which apparently digest milk in much the same manner, but have appar- 

 ently no influence whatever upon the growth of the lactic bacteria. This would 

 indicate perhaps that instead of some of these main products of digestion, which 

 are indicated in our discussion as being the cause of the facilitated growth, that 

 a secondary product, which is not apparent at all in our analysis, is the real 

 stimulant of the lactic bacteria. 



We can further say that no acid is produced by germ B, which we have studied 

 so thoroughly. Although when grown in milk, germ B will in time curd the 

 milk upon heating, we have demonstrated that it is not due to the presence of 

 any acid, but to other products which are found in the digested milk. Besides 

 germ B producing a favorable action upon the lactic bacteria, we have met with 

 several others which are also capable of doing the same thing, but varying in 

 degree only. Out of ten wliich we have partly studied, six are capable of favor- 

 ably influencing the lactic germs. 



It is also interesting to note how much association may influence the butter 

 products. Mr. Wright has conducted some experiments in which he has demon- 

 strated that in order to cover up the disagreeable odor and taste produced by 

 germ B it is necessary to employ 45 per cent of good starter in the ripening 

 of cream. It is desirable, perhaps, to introduce at this point a summary of Mr. 

 Wright's work. ^'i 



