476 Transactions of the Canadian Institute. [Vol. VII. 



in a few weeks, completely disappeared. In no cases was it present in 

 large numbers. 



Comment has already been made upon the fact that by far the 

 largest number of species determined in all the samples tested, were 

 lactic acid species, and that other species, although more or less con- 

 stantly present, were not invariably so, and never in very large quantities. 

 This is a most important, practical consideration, for it means that, 

 although by the most scrupulous care, it may not be possible to procure 

 milk free from germ-life because of those that are present in the udder 

 of the cow, yet the species that gain access to the milk through this 

 source are, for the most part, beneficial ones. In Bulletin No. 21, 1900, 

 of Storr's Agricultural Experimental Station, Conn speaks of a method, 

 now widely adopted in American dairies, for procuring what is known 

 as a " natural starter." The method consists in drawing milk, just as 

 has been done in all the examinations we have made, into sterilized 

 flasks, and using cultures from these as starters. Conn says, " there can 

 be no question that the use of natural starters thus made has been a very 

 decided advantage to the buttermaker," for the reason that " the 

 bacteria which are within the cleanly cow's udder and thence get into 

 the milk, are most commonly of the desired character." There is, no 

 doubt, some uncertainty about this method, but so far as all examina- 

 tions conducted by us are concerned, the cultures so obtained would be 

 good ones, being largely composed of lactic acid species. 



While the large per cent, of lactic acid species present is the 

 paramount characteristic of the bacterial flora of freshly drawn milk, yet 

 there are other peculiarities of considerable, if not equal, importance. 



By reviewing the description of the species determined, it will be 

 noted in every case that, although each species would grow at room 

 temperature, yet the optimum temperature was in the neighbourhood of 

 37°. This fact was well demonstrated in comparing gelatin plates, made 

 from the general milk supply, with those made from the aseptically 

 drawn milk. These plates cannot be kept at a temperature higher than 

 22°, and it was most marked that when plates from the former were quite 

 covered with bacterial growth, those from the latter were still clear. On 

 the other hand, when agar plates were used and kept at a temperature 

 of 37°, the order of growth was slightly reversed. This explains facts 

 that were noted in reference to the keeping quality of the aseptically 

 drawn milk, as compared with that of the general milk supply ; for, 

 when kept at room temperatures, the former remained good considerably 

 longer than the latter ; whereas, when kept at ^7", both became curdled 

 in less than twenty-four hours. 



