230 STATE BOARD OF AGRICULTURE. 



Numerous plates were made from the dust floating in the air of the 

 stable, from the particles of filth falling from the nether regions of a 

 cow and her udder, and from the milk house or dairy. By means of the 

 apparatus described in Bulletin 140, p. 101, the milk from the milk duct 

 was studied. 



After the plates made from these different sources had developed, the 

 colonies were studied closely and bouillon cultures made from the differ- 

 ent kinds. These were subjected to the stated Pasteurization after they 

 had grown for several days, and two or three days after Pasteurizing, 

 transplantations were made into sterile bouillon tubes, using three 

 platinum loopfuls for each inoculation. If any of these latter tubes 

 developed, they were regarded as bacteria resistant to Pasteurization. 



This work may be tabulated as follows: 



In the dust from the stable, 2 were found out of 20. 



In the dirt from the cow, 2 were found out of 24. 



In the dust from the dairy, 1 was found out of 15. 



In the fore milk of the milk-duct, 3 were found out of 25. 



From this we may expect to find resistant bacteria in the dust of the 

 stable, in the filth from the cow, in the dust of the dairy and in the milk- 

 duct of the teat ; in fact, we may expect them from almost any source to 

 which the milk is exposed. 



3. The Study of Their Actions Upon Milk. 



What the bacteria may do when left after Pasteurizing is interesting, 

 because it has been supposed that the lactic acid bacteria have been 

 killed. This is largely true but not universally. The keeping quality 

 of the milk is only slightly enhanced, and yet the changes which follow 

 Pasteurization are markedly different. Normally, milk sours from the 

 growth of the lactic acid bacteria, but when these bacteria are killed 

 other varieties act and most of these may be* said to peptonize or digest 

 the casein of the milk, making the milk as clear as water. This digestion 

 is simply the conversion of the insoluble casein into the soluble form 

 caseon. Before this digestion, in some cases, the milk is curdled by a 

 ferment secreted by the bacteria. Again, the milk is curdled by acid 

 formation without any digestion, as in the usual lactic acid fermenta- 

 tion. A few bacteria are found which produce no change whatever to 

 the naked eye. 



The following tables will illustrate the different actions of the species 

 isolated : 



+ = Affirmative. 

 — = Negative. 



Those bacteria which curdle the milk only. 



3 6 9 29 30 32 38 43 44 45 46 48 60 



— — — — — + 



62 107 112 115 116 117 



