122 EXPERIMENTAL DAIRY BACTERIOLOGY 



Exercise. Each student will examine samples of milk for leucocytes 

 from healthy animals, and, if possible, from animals having garget. 

 Both methods should be employed on the same sample, if possible. 

 Compare results obtained by the different methods. 



Examination for fibrin. In inflammatory troubles of the 

 udder white blood corpuscles are not the only constituent of 

 the blood passing from the blood vessels into the glandular 

 tissue and milk ducts. The blood serum, with its dissolved 

 constituents, serum albumen and fibrinogen, passes out to a 

 greater or less extent. Under appropriate conditions the fibrin- 

 ogen is changed to the insoluble fibrin, which, when present 

 in any considerable amounts, can be detected by microscopic 

 examination. The fibrin determines the distribution of the 

 leucocytes. When fibrin is present in small quantities or not 

 at all, the leucocytes are evenly distributed. In the presence 

 of fibrin larger or smaller clumps are to be found. 



The milk may be centrifugalized, as in the smeared-sedi- 

 ment method for leucocytes. The sediment should be spread 

 on a slide, noting whether any dough-like material is present. 

 The smear is stained as follows, after being allowed to thor- 

 oughly air dry : Flood with aniline-water gentian violet (p. 43). 

 Allow stain to remain on the preparation for five minutes, and 

 then wash. Flood with iodine solution (p. 43), wash off after 

 one or two minutes, and add aniline oil from time to time 

 until the color is completely discharged, as shown by the color- 

 less condition of the oil. Wash in water, dry, and examine. 

 The fibrin should appear as threads stained dark purple. 



Exercise. The student should familiarize himself with the appear- 

 ance of fibrin in blood. Examine normal milk for fibrin ; also that 

 from an animal having garget. 



Direct enumeration of bacteria in milk. In control work, 

 such as must be carried on in the municipal laboratories of 



