120 EXPERIMENTAL DAIRY BACTERIOLOGY 



gives the number per cubic centimeter in the original milk. 

 The factor 200,000 is obtained as follows : The leucocytes 

 are concentrated in 1/20 part of the milk. In order to de- 

 termine the number in each cubic centimeter of the milk, the 

 number found in 1/4000 cu. mm. of the liquid examined must 



be multiplied by - ^ , or 200,000. ' 



The student should become familiar with the appearance 

 of white blood corpuscles by the examination of blood. Blood 

 is easily obtained by winding a rubber band about one finger, 

 and when the veins are gorged with blood, pricking oneself at 

 the base of the nail with a glass rod drawn out to a fine point. 

 The puncture should be made by a quick stroke. The drop of 

 blood is mixed with nine volumes of 0.3 per cent glacial acetic 

 acid and examined in the blood counter. The red corpuscles 

 will be scarcely visible in this form of preparation. 



Examination for leucocytes ; smeared-sediment method. 

 Small glass tubes closed at either end with soft rubber stop- 

 pers are used. The tubes should be of 6 mm. internal diam- 

 eter and of sufficient length to hold 2 cc. When filled with 

 milk, which has been heated as in the Doane-Buckley method, 

 they may be centrifugalized in any form of centrifuge. A flat 

 aluminum disk, with upturned edge, may be attached to an 

 ordinary centrifuge. The disk is provided with appropriate 

 clamps for holding the small tubes in position, and with a 

 cover held in place by a screw. With this form of centri- 

 fuge head much greater speed can be attained, since the air 

 resistance is much less than with the ordinary tubes. A 

 source of power that would produce 1200-1500 revolutions 

 per minute with the ordinary head will produce 3000 with 

 the disk.. Twenty samples may be centrifugalized at once 

 in an apparatus of this kind. 



