New York Agricultural Experiment Station. 113 



of about 50 per ct. Such variations in the amount of milk taken 

 make a serious error in the final computation. 



In addition to these objections, the Brownian movement of stained 

 particles in the milk occasionally makes it difficult to distinguish 

 them from the smaller bacteria. Rosam's preparations must be 

 examined at once as they are not permanent. This is also an 

 objection in practical work where it is often impossible to count 

 the bacteria at once, particularly if many samples are being inspected. 



The value of a similar method of making milk preparations as 

 a means of counting tissue cells has been known since 1905, when 

 Doane and Buckley 14 suggested a method of staining and making 

 slides, preferable in both respects to the method suggested by Rosam. 



PRACTICAL APPLICATION OF MICROSCOPIC METHOD OF 

 EXAMINING DRIED MILK SMEARS. 



It is impossible to say definitely how much practical use can 

 be made of the microscopical examination of dried and stained 

 milk smears. Further investigations must be made to show whether 

 the results here obtained agree with those found by other investi- 

 gators working under different conditions. Thousands of counts 

 must be made before the usefulness of the method can be fully 

 established. 



Other questions of great importance which remain unsolved in 

 any satisfactory way are: How rapidly do dead bacteria undergo 

 dissolution in milk? Can they be distinguished from living ones 

 by means of stains or other technique? These questions must be 

 answered before the technique can be used in a practical way for 

 the examination of pasteurized milk, or for milks where so large 

 a number of bacteria have developed that many have died from one 

 cause or another. 



All that can be said is, that this technique is one which shows 

 much promise under the conditions where it has been tried. It 

 is a means whereby milk dealers, butter-makers and cheese-makers 

 can quickly determine the exact bacterial condition of a given 

 sample of milk. In all of these cases it is hoped that it will serve 

 a double purpose: First, to enable a farmer who really produces 



14 Doane, Charles F. Leucocytes in miJk and their significance. Md. Agr. Exp. 

 Sta., Bui. 102, 1905. 



8 



