No. 7. DEPARTMENT OF AGRICULTURE. 647 



1. The cow. 



a. Internal. 



b. External. 



2. Air. 



3. Utensils. 



4. Attendants. 



5. Age. 



It is impossible to tell which of these is the most serious. They 

 are like the links of a chain. 



The contamination within the cow's udder may be of an exceed- 

 ingly dangerous kind if she is not in good health. Even though the 

 cow's udder seems to be normal, if her general condition is not good, 

 her milk should be rejected as a human food. The presence of pus 

 cells in milk taken from inflamed udders is a form of contamina- 

 tion that has received much attention quite recently. We are in- 

 formed that these organisms in large number render the milk most 

 objectionable as a food. The old idea that milk is germ-free so 

 long as it remains in the udder has been disproven. Bergey reports 

 that his investigations show that about one-third of the large num- 

 ber of samples of milk taken from the udder with aseptic precau- 

 tion, were free from bacteria. The other two-thirds were more or 

 less contaminated. About one-tenth of the samples contained more 

 than 5,000 bacteria per cubic centimeter. His investigations showed 

 that the organisms most commonly found within the udder are those 

 associated with an inflammatory condition of the tissues. The 

 larger part of bacteria in the udder can be avoided by discarding 

 the fore milk. Contamination of milk from the hide and hair of 

 the cow results in the introduction of some very objectionable forms 

 of bacteria, including many that cause putrefactive changes in the 

 milk and secrete products which are more or less irritating and even 

 poisonous. 



A series of carefully conducted experiments has shown that con- 

 tamination of this kind can be very greatly reduced by the simple 

 precaution of cleaning the cow's udder. This may result in avoid- 

 ing about 75 per cent, of the dirt and bacteria that would fall from 

 an udder in ordinary conditions. 



The air of the stable always contains more or less small particles 

 of dust and these carry with them bacteria. They are carried up 

 by movements of the air due to.drafts, disturbances of dry feed and 

 bedding, etc. These particles of dust are settling like a constant 

 shower and an open milk vessel catches a surprisingly large number 

 of tliem. In a study upon this subject. Professor Eraser, of the Illi- 

 nois Experiment Station, exposed more than 1,000 petri plates. He 

 found that the number of bacteria or bacterial clusters, falling in a 

 few seconds onto a petri plate exposed in barnyards varied from 

 to-86. Just after a shower, when the dust was settled and the 

 air was clean, there was practically no contamination. On a dry 

 day when the wind was moving the dust more or less, the contamina- 

 tion was highest. The petri plate exposed in a vacant stable showed 

 27 colonies while another exposed after the cows had been admitted 

 showed 68 colonies, and the third exposed very near the floor showed 

 718 colonies. An exposure in two feed rooms just after bran was 

 let down showed 418 colonies, and three minutes later only 6. In 



