LABORATORY WORK IN DAIRY BACTERIOLOGY 287 



from the surface with a bit of cotton on the end of a rod, being 

 careful not to leave any of the cream in the tube. By means 

 of a small siphon remove the milk, keeping the tip of the tube 

 just below the surface so as to avoid disturbing the sediment. 

 Siphon away the milk to within about one-eighth of an inch 

 of the sediment. Add two drops of a saturated alcoholic solu- 

 tion of methylene blue to the tube, and, after thoroughly mixing, 

 place the tube in boiling water for two minutes to aid the stain- 

 ing. Add enough water to bring the total bulk either to one 

 or two c.c., according to the amount of sediment. This will 

 give a blue mass of stained sediments. To count their number 

 an ordinary blood counter is used. This will have a counting 

 chamber marked off into squares and holding exactly one-tenth 

 of a cubic millimeter. Fill this counter with the stained sedi- 

 ment, cover with a cover-glass, allow to stand for about one 

 minute for the leucocytes to settle, and then, placing under a 

 microscope, count the number of leucocytes found in a single 

 ruled square and calculate the numbers in the whole chamber. 

 Remembering then that the chamber contains one-tenth of a 

 cubic millimeter of the stained sediment, it is easy to calculate 

 the number of leucocytes in the original milk. This should be 

 calculated upon the basis of a certain number per c.c., and good 

 milk should not have more than 500,000 per c.c. 



No. 19. Staining of Tubercle Bacilli. The staining of tubercle 

 bacilli is rarely needed in dairying, but it is sometimes useful. 

 The method is as follows. Make Carbol Fuchsin as follows: 



Basic fuchsin ". I part. 



Absolute alcohol 10 parts. 



Carbolic acid (1-20 of water) . . . 100 parts. 



Prepare, also, a 20% solution of hydrochloric acid in water. 



Spread the specimen to be stained (sputum or milk sediment 

 from a centrifuge in the last experiment) upon a glass slide, 

 and dry slowly in moderate heat. After drying, flood the slide 



