128 THE AMERICAN MONTHLY [May 



Formalin as a Reagent in Blood Studies. 



ERNEST I. KTZER 



Among the most common reagents used in the demon- 

 stration of blood corpuscle structure, are found osmic acid, 

 salt solutions, picric acid and acetic acid. But all of these 

 cause distortions of the corpuscles, so they art imperfect 

 fixing agents and preservatiTes. The method of drying 

 blood on the coverslips is seldom successful in the hands 

 of beginners. Formalin has been found very useful in 

 this connection, both as a fixing agent and as a preserva- 

 tive, because it produces no appreciable distortion of cor- 

 puscles, does not interfere with staining, is easily opera- 

 ted and preserves blood perfectly, at least, for several 

 months. 



The method consists of the following steps : Mix one 

 volume of perfectly fresh blood with three volumes of a 

 two per cent solution of formalin. Allow the mixture to 

 stand at least an hour ; then draw a small quantity from 

 the bottom of the vessel with a pipette, by which a drop 

 is transferred to a clean coverslip ; spread evenly over the 

 coverslip and allow the liquid to evaporate. The method 

 of pressing the coverslips together, as in sputum analy- 

 sis, is to be preferred. Pass the coverslips through the 

 flame, films uppermost, in order to cement the corpuscles 

 to the glass. Dip into a fire per cent solution of acetic 

 acid once or twice. Remove the acid with water. 



The best stain for non-nucleated corpuscles is Gentian 

 violet (a two per cent solution ; time of staining,about two 

 or three minutes). For nucleated forms, contrast stains, 

 as Methyl blue and Gentian violet, or Hematoxylin and 

 Eosin, or Methyl green and Safranin, give very good re- 

 sults. Ehrlich's Triple stain may be used for human cor- 

 puscles. Wash out excess of stain with water or alcohol 

 as the stain requires. Remove alcohol with clove oil or 

 xylol, and mount in Canada Balsam. 



