THE BLOOD. 59 



hold it over a flame, being careful not to ignite the paper, until the film 

 turns brown. The blood is now properly affixed, and may be stained 

 by the following method: 



No. XL Scheme for Staining Blood Preparations. 



(1) Make a cover-glass preparation and affix by the method given 

 above. 



(2) Using Cornet forceps, stain with alcoholic or glycerine eosin, 

 thirty minutes to one hour. 



(3) Wash off eosin by dipping cover-glass vertically into distilled 

 water one or two times. 



(4) Apply Delafield's haematoxylin fifteen minutes. 



(5) Wash in water, dry with gentle heat, and mount in balsam. 



(6) Label and study. 



Observe that the colored discs are stained red by the eosin, while the 

 nuclei of the leucocytes are stained blue by the haematoxylin. Find sev- 

 eral lymphocytes and compare the sizes of their nuclei. Study the poly- 

 nuclear elements. How many nuclei do you find? Make drawings to 

 represent the red corpuscles on edge and in profile, rouleaux, crenation, 

 fibrils of fibrin, lymphocytes, and polynuclear elements. 



Laboratory exercise No. 14. Staining for Plasmodium malariae. 



(1) Make a cover glass preparation from a malarial patient by the 

 usual method. 



(2) Stain with alcoholic methylene blue, fifteen minutes. 



(3) Wash in water and examine. 



(4) Dry, mount and label, if a good specimen. 



Search for the organism in the red corpuscles, also in the plasma. 

 It has no definite form, but may be semi-lunar, spindle-shaped, spher- 

 ical, etc. It can be recognized by its color, the discs not taking the 

 blue stain. 



Laboratory exercise No. 15. Counting the Uood corpuscles. Probably 

 the most satisfactory device for counting the corpuscles is by means of 

 the centrifuge. Pursue the following method: Attach to the graduated 

 blood tube a piece of rubber tubing. Having secured a large drop of 

 blood, fill the graduated tube by gentle suction, and then place it in the 

 ha3matokrit, making the bearings secure. Revolve the handle of the 

 centrifuge seventy-seven times in one minute. This will give 5,000 rota- 

 tions of the haematokrit, resulting in the precipitation of the red cor- 

 puscles to the outer end of the tube, the leucocytes being arranged next, 

 and the plasma filling the other end. If the red corpuscles fill half the 

 tube, standing at the graduation marked " fifty," it indicates that there 

 are 5,000,000 corpuscles in a cubic millimeter of the blood; if it stands 

 at the mark " thirty-five," there are 3,500,000 in a cubic millimeter. The 

 numbers given above indicate the normal amount of corpuscles for man 

 and woman respectively. Should there be less than the normal number, 

 it indicates anaemia. Should there be the required number of red disks, 

 but too many leucocytes, there is an indication of leukaemia. What 

 other method may be employed for counting corpuscles? 



