298 



STATE BOARD OF- AGRICULTURE. 



TEST III. 



After milking. 

 After 4 hours., 

 After 8 hours.. 

 After 13 hours 

 After 18 hours. 

 After 26 hours. 



Confined. 



1,280 



4,650 



76,950 



2,779,300 



41,105,750 



333,939,000 



Exposed 

 over glass. 



1.280 

 5,120 



557,950 



15,582,000 



66,301,750 



454,522,000 

 curdled. 



Exposed 

 over tin. 



1,280 



9,400 



1,236,750 



21,036,500 



90,782,560 

 curdled. 

 724,632,000 



In the above tables it will be very apparent that the confined conditions of milk tend 

 to reduce the number of bacteria. Milk exposed to air far exceeds the number of germs 

 in unexposed milk. Compare too the milk exposed over glass and the milk exposed 

 over tin and the tin receptacle seems to favor the development of bacteria. This cor- 

 responds very closely to the previous tables in which a study of the production of 

 acidity has been made. Why tin under these conditions favors the development of 

 bacteria over the development of bacteria in a glass receptacle, unless the tin combines 

 with carbon dioxide and also reduces the amount of lactic acid, is difficult to explain 

 inasmuch as there appears to be some germicidal action instigated by bringing media 

 in contact with metals. One factor, however, remains. In the case of tin we have a 

 dark vessel and in the case of glass the entrance of light rays, although in a semi-dark 

 room, may account for the reduced numbers in the glass vessel below those in the tin 

 vessel. This hardly seems credible, however. The explanation will probably be found 

 in the affinity of the tin surface for carbon dioxide and lactic acid. 



An attempt was further made to ascertain whether by growing the plates, made from 

 the milk in confinement, in hydrogen would increase the number of colonies developing. 

 Several tests thus made only served in reducing the number of colonies instead of increas- 

 ing them. We can understand this decrease to be due to the action of hydrogen. 



XXIX. DOES AERATION INFLUENCE THE GERMICIDAL ACTION OF MILK? 



This interesting action of milk should not be passed over without showing the 

 possible influence aeration may have upon it. The impetus given to this work by 

 Conn and Hunziker led me to attempt to ascertain whether milk unexposed to the 

 air Avould have a greater or less germicidal action than milk exposed to the air. Sevei'al 

 tests were made, six of which are recorded below giving the results in detail. The milk 

 was secured with the apparatus used in study of the gas-content of milk without 

 exposure to air. 



TABLE XXV. 



DOES AERATION INFLUENCE THE GERMICIDAL ACTION OF MILK? 



