302 THE EXAMINATION OF MILK 



2. Blood ; Leucocytes ; " Pus-cells." Red blood 

 corpuscles, and white corpuscles or leucocytes and " pus- 

 cells " are not uncommon in milk. 



The presence of blood may arise through temporary 

 rupture of a small blood vessel in the udder, or may 

 come from more serious lesions connected with disease 

 of the gland. The red corpuscles in such cases may be 

 sufficient in number to colour the milk. When present 

 they may be easily recognized on microscopic examina- 

 tion of the sediment thrown down in the milk after it has 

 stood for a time. They are circular bi-concave disks, 

 without nuclei, from 6 to 8 ^ in diameter, and of pale 

 yellowish tinge when viewed singly. 



On account of their form, light is unequally transmitted 

 through them, the centre appearing brighter or darker 

 than the surrounding border, according as the focus of 

 the microscope is altered. When abundant they may be 

 seen piled closely together in " rouleaux " like coins. 



The colourless corpuscles or leucocytes are larger 

 spherical protoplasmic structures, over 10 t& in diameter 

 present in the blood and lymph of animals. They con- 

 sist of granular protoplasm and contain one or more 

 nuclei : in a living state they exhibit amceboid move- 

 ment their outline constantly changing in form. Under 

 certain conditions many of the leucocytes pass through 

 the walls of the capillary blood vessels into the sur- 

 rounding tissues; this is especially the case at points 

 where there is inflammation. The pus or " matter " 

 which accumulates in wounded or inflamed areas con- 

 sists largely of dead, altered, or degenerate leucocytes, to 

 which the term " pus-cells " has been applied. 



The exact significance of leucocytes in milk is a 

 matter upon- which there is much difference of opinion. 



