894 Popular Editions of Station Bulletins of the 



First of the bodies that may be seen when milk is 



Fat globules properly exposed under the compound microscope 



in milk are the fat globules. These are normal secretions 



studies. of the udder and form an essential, though varying, 



proportion of all milk. Milk fat is very highly 



prized in human dietaries; so that the quantity of fat globules present 



in milk has come to serve as an index to its quality. Their amount 



can, however, be easily and accurately determined by a chemical 



method, the Babcock test; and microscopic study of them is not 



now considered so essential as at one time. Such study was very 



useful in early work on milk, in establishing the nature of these 



globules, and is still helpful in working out certain problems, like 



those of churning. In the most valuable microscopic work with milk, 



though, the fat globules are a detriment; since they are comparatively 



large and cover or obscure the other microscopic objects it is desired 



to study. Accordingly, in such work the fat must be dissolved. 



This is one step in a new method of microscopic examination of milk 



now in use at the Station, whereby the other two classes of minute 



objects are made to stand out clearly in the field of vision. 



Of these two classes, the cells should properly 

 Cells in be placed first since they are, like the fat globules, 

 milk. normal constituents of all milk and are derived from 



the udder. These cells are discharged at all times in 

 varying numbers. The fluctuations may or may not indicate dis- 

 eased or abnormal conditions in the udder, therefore the changes in 

 number may become an index to the sanitary quality of the milk. 

 Though placed third among the microscopic 

 Bacteria bodies found in milk, because they are not normal 

 in milk. constituents of it — are not produced by the udder 

 but find their way into the milk after it is secreted — 

 bacteria should really be considered first, for they are, without 

 doubt, most important of all, at least from a sanitary standpoint. 

 Though not essential components of milk, bacteria are almost 

 universally found in it, even in the udder, and they exert a more 

 immediate and greater influence toward change than any of the 

 normal milk constituents. They are living organisms and make 

 milk both their food and the scene of most diverse vital activities; 

 so that each type of bacterium may change the milk materially, 

 either for good or for ill. 



Because of the importance of microscopic bodies 



Prescott-Breed in milk and because these have, until recently, 



microscopic been most studied by indirect methods, there seems 



method of much promise in a new plan of attack, originated 



milk study, by Prof. Prescott, of the Massachusetts Institute 



of Technology, and Dr. Breed, now of this Station. 



This method has already been used in two extensive series of studies 



made at the Station. 



