2086 Journal of Applied Microscopy 



The Bacterial Flora of Freshly Drawn Milk. 



II. 



Comment has already been made upon the fact that by far the largest num- 

 ber of species determined in all the samples tested were lactic acid species, and 

 that other species, although more or less constantly present, were not invariably 

 so, and never in very large quantities. This is a most important practical con- 

 sideration, 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, March, 1900, 

 of Storrs Agr. Expt. Sta., 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 

 made for this work 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 teats and thence get into the milk, 

 are most commonly of the desired character." There is no doubt some uncer- 

 tainty about this method, but so far as all examinations conducted by us are 

 concerned, the cultures so obtained would be good ones, being largely composed 

 of lactic acid species. 



While the large percentage 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 temperatures, yet the 

 optimum temperature was in the neighborhood of 37°. This fact was well dem- 

 onstrated in comparing gelatine 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 tempera- 

 ture 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 tempera- 

 tures the former remained good considerably longer than the latter ; whereas, 

 when kept at 37°, both became curdled in less than 24 hours. 



Another marked characteristic of all the species was that they were faculta- 

 tive anaerobes. This anaerobic faculty was especially marked in the species, Nos. 

 I, II, and III, that were found to be so uniformly present in all the milk tested. 

 This is just what one would naturally expect, for the conditions in the udder 

 must be largely anterobic conditions. The presence of anaerobic conditions and 

 a high temperature are a most wise provision, favoring as they do, in a marked 

 manner, the multiplication of lactic acid species to the exclusion of many other 



