Chapter XIV: Blood 99 



NOTE. In the clinical examination of blood great care must be exer- 

 cised to have it absolutely fresh ; furthermore, the cover-glasses should 

 be handled with forceps instead of by means of the fingers. It is recom- 

 mended that one pair of the forceps be Coronet or spring forceps of some 

 kind (Fig. 39). The lobe of the ear is perhaps the best region from 

 which to obtain the blood. The needle with which the puncture is 

 made should always be sterilized. Wipe away the first drop of blood 

 that appears. The drop finally chosen should be one that has appeared 

 immediately after the spot has been wiped and it should be but little 

 larger than a pin-head. The whole operation cannot be performed too 

 rapidly. To shorten the time it is well to have an assistant to prick and 

 manipulate the ear while the operator attends to the preparation of the 

 film. 



3. When several satisfactory films have been prepared, place them 

 on the heated bar as indicated in step 1. Cover them to keep out dust 

 and leave them for from 30 to 60 minutes. 



4. Remove the covers and stain the preparations 15 or 20 minutes 

 with Ehrlich's triple stain (reagent 39, Appendix B) by flooding the film 

 with the stain by means of a pipette. Rinse off the surplus stain with 

 water, blot the film with blotting paper and dry it by holding it with 

 the edge downward high above the flame. When dry, mount in balsam 

 on a slide. 



NOTE. Instead of heating the preparation, much the same results 

 may be obtained by subjecting films (prepared as in step 2) to ether- 

 alcohol (reagent 16, Appendix B) for from 1 to 12 hours, drying them 

 again in the air and then staining as above. 



b) Rapid method. 1. Prepare a film as above (a 2), only, before it has 

 dried treat it with concentrated aqueous solution of corrosive sublimate 

 (reagent 13, Appendix B). 



2. Wash the preparation thoroughly in water or in 50 per cent, alcohol. 



3. Stain for 10 minutes in Delafield's or Ehrlich's hematoxylin (reagent 

 49 or 50, Appendix B), rinse in 70 per cent, alcohol and stain for 20 sec- 

 onds in eosin (0.5 per cent, solution in 70 or 95 per cent, alcohol). 



4. Rinse in 95 per cent, and in absolute alcohol each for 2 minutes, 

 pass through xylol and mount in balsam. 



After rinsing following staining, some workers simply blot the prep- 

 aration with blotting paper, dry it in the air and mount it in balsam. 



III. ENUMERATION OF BLOOD CORPUSCLES 



" The instrument used is the hemocytometer (Fig. 37). Obtain a drop 

 of blood from the lobe of the ear or from the finger. Fill the clean 

 pipette of the hemocytometer to the mark 1 by careful suction. (If the 

 blood is drawn beyond the 1 mark, blow it out immediately, clean the 



