127 



SPECIAI. METHODS. 



THE BI^OOD. 



§ 1 19. Special methods in the examination of the blood include 

 (i) Examining fresh ; (2) Technic of staining blood films; (3) 

 Determination of the number of red and white corpuscles per cubic 

 millimeter ; (4) Determination of the relative amount of hemoglo- 

 bin ; (5) Spectroscopic examination of blood (hemoglobin), (i) 

 and (2) are briefly given here ; for (5) see Microscopical Methods, 

 §§ 201-203. 



§ 120. Examining fresh. This consists in covering a drop 

 on a slide and immediately sealing the cover-glass to prevent evapo- 

 ration, observing the following cautions: (i) The drop of blood 

 (from the finger or the lobe of the ear) should flow freely and not 

 be obtained by pressure. The drop should be a medium-sized one, 

 which will spread out in an even, thin layer under the cover. (2) 

 The drop should be received upon a cover or slide, covered, and 

 sealed at once with castor oil. 



Examination of fresh blood may be used in clinical examination 

 for the detection of some abnormal conditions, and it is of value in 

 the rough diagnosis of many others. 



§ 121. Stained preparation of blood, (a) Preparing the 

 blood film. This may be best done in one of two ways : (i) The 

 edge of a slide is first drawn through a drop of fresh blood and then 

 moved quickly across the surface of a clean cover-glass, in this way 

 spreading the blood in a thin, even layer upon the cover. Success 

 depends upon getting the right amount of blood upon the edge of 

 the slide and the quick, even movement by which it is spread upon 

 the cover -glass. A second, possibly better, method is the following : 



(2) Have ready two thin clean cover-glasses and obtain a drop 

 of fresh blood. Take one of the covers in the forceps, touch it to 

 the drop of blood and place it upon the second cover-glass eccentric- 

 ally, with one edge projecting slightly. Slip the two covers apart 

 in the plane of their surfaces and dry them quickly by waving them 

 in the air or by passing them rapidly over the tip of a flame. The 

 lower cover-glass will have the better film. 



(Jj) Fixing the hemoglobin with (a) ether-alcohol or (b) heat. 



