MICROSCOPICAL DIAGNOSIS. 25 



BLOOD. 



IF a drop of blood should be placed on the slide, covered with 

 the thin glass and transferred to the microscope, the examina- 

 tion would be anything but satisfactory. The number of corpuscles 

 in the field would be so great and the number of layers so many 

 that the specimen could not be studied to advantage. Again, if 

 mixtures be used to dilute the blood, unless prepared with the 

 greatest care, the corpuscles will be materially changed in appear- 

 ance. 



When a comparatively short examination is required, the fol- 

 lowing method will prove satisfactory: To procure the drop of 

 blood, one of the fingers is congested by tying around its base a 

 string or handkerchief; when well filled with blood, a fine cambric 

 needle is thrust quickly through the skin over the end of the con- 

 gested finger; one surface of a glass slide is now gently breathed 

 upon, and this slightly moistened surface brought in contact with a 

 drop of blood, just pressed from the puncture; one surface of the 

 cover-glass is also breathed upon and its edge placed close to, just 

 in contact with the edge of the drop of blood, and with the aid of 

 a needle the cover is lowered away from the drop not over it 

 until it comes in contact with the slide; the blood-corpuscles will 

 readily flow between these moist glasses, by capillary attraction, 

 until the surface beneath the cover-glass is nearly or entirely cov- 

 ered; prepared in this way, there is but one layer of corpuscles and 

 the whole specimen shows to the best possible advantage. 



For this method to be successful it should be carried out rapid- 

 ly and the moisture should not be in excess, as water causes changes 

 in the corpuscles; yet it should be sufficient to allow the corpuscles 

 to flow readily under the cover. The amount is soon learned after 

 one or two trials. If the examination is to continue for some time 

 a layer of oil can be placed around the cover-glass to prevent the 

 drying of the specimen. 



