78 VERMONT DAIRYMEN'S REPORT. 



so few that they escaped detection until incubated, when their 

 presence finally became known by the curdling of the milk.) 



It will thus be seen that even without milking tubes it is 

 possible to draw milk which is practicall)- bacteria free, if the 

 dust, hair, etc., are kept out. 



At the same time that the above milk samples were taken, I 

 exposed a gelatine plate in the stable for two minutes and found 

 by the colonies developing on it that during that time several 

 thousand bacteria had been deposited thereon with the settling 

 dust of the stable. 



City milk contains on the average from seven to ten million 

 bacteria per cubic centimeter, and we all know that the keeping 

 quality and healthfulness of such milk is not all that it should 

 be, for although when kept cold no apparent change takes place, 

 yet as Prof. Sedgwick and Mr. Marshall have shown, there is a 

 slow yet constant increase of bacteria that ultimately give rise to 

 putrefaction, even though no souring change occurs. If the same 

 milk, on the other hand, had been allowed to remain warm even 

 for a short time, the lactic acid bacteria would have developed 

 and the milk would have soured. So although bacteria may be 

 retarded in their growth by icing, yet, iced or not, either putre- 

 factive bacteria or lactic acid bacteria are bound to develop. 



Many of the aerator advertisements claim that aeration will 

 remove bacteria from milk and so prevent its souring, but the 

 real benefit derived from aeration comes from the fact that the 

 milk being charged with air favors the growth of other than the 

 souring bacteria which thrive best when growing without air. 

 Thus while aeration undoubtedly prevents souring to a great 

 extent, yet on the other hand it favors the growth of per- 

 haps the less desirable putrefactive bacteria, besides at the same 

 time being likely to introduce large numbers of bacteria from the 

 air as it conies in contact with the milk, especially if the aerator 

 is placed in a stable or tie-up, as is commonly done by the aver- 

 age farmer. 



With Messrs. H. P. Hood & Sons I have been enabled to 

 visit a few dairies during the past year, and to attempt to 

 trace the cause of the many high numbers of bacteria 

 we found in the milk from them as received in Boston. 

 With the dairies in question, the following was the 

 method of procedure. We first made bacterial anatyses each 

 week until we knew what to expect from any given dairy that 

 we were investigating. With this knowledge gained I visited 

 the dairies and sought to find out the cause of the excessively high 

 or low number of bacteria I had found, and in nearly every case 

 was able to discover the reason. 



The following tables give a general idea of the bacterial con- 

 tent in the milk found in ten dairies examined. The different num- 



