and Laboratory Methods. 2039 



A Review of the Methods of Staining Blood. 



II. 



B. Fixing Dry Blood Films. 



The fixing processes applied to dry blood films are for the purpose of coagu- 

 lating the albuminous substance of the blood which cements the corpuscles to 

 the cover-glass and prevents them from being washed off or the hemaglobin 

 from being dissolved out of the red corpuscles in the process of staining. The 

 treatment for this purpose varies with the method of staining. Many of the 

 eosin-methylen blue neutral compounds require no previous fixation, this being 

 accomplished in the process of staining. The neutral tri-color stain of Ehrlich 

 and its modifications require but slight previous fixation. On the other hand, the 

 basic dyes and especially the acid dyes require thorough fixation before staining. 

 Moreover, different stains require different methods of fixation. The basic dyes 

 act more satisfactorily after chemical fixatives, but the acid dyes should be pre- 

 ceded by dry heat, and many staining solutions require special methods of fixa- 

 tion. Fixation of dry blood films is accomplished by the various application of 

 two agents, dry heat and chemicals. 



DRY HEAT. 



Dry heat is the fixative used by Ehrlich for dry blood films. Various ways 

 have been devised for applying the proper amount of heat. 



1. Passing the Preparation through the Flame. — This is the method of bacteri- 

 ologists for fixing dry preparations of bacteria to the cover-glass. The cover- 

 glass, held by forceps, is passed three or four times slowly through the flame of 

 a Bunsen burner or alcohol lamp. It rarely gives satisfactory results for blood 

 preparations. 



2. Heating above the Flame. — This method gives better results than the pre- 

 ceding, but is not to be recommended except in case of haste. The cover- 

 glass is held by its edges between the thumb and forefinger as low over the flame 

 of the Bunsen burner as one can bear the heat for thirty seconds. 



3. Heating on a Metal Plate, — The flame of a Bunsen burner or an alcohol 

 lamp is placed under one end of a metal plate supported on a tripod stand. After 

 an equilibrium between heating and radiation has been attained, the preparations 

 are placed blood side downward at a position on the plate a little nearer 

 the flame than where a drop of water is at once converted to steam, and allowed 

 to remain from fifteen minutes to an hour. 



Rubinstein (1897-8) endeavored to determine a position of optimum tempera- 

 ture for quickly fixing blood films on the metal plate. If a drop of ^vater be 

 allowed to fall on the metal plate sufficiently near the point of application of the 

 heat it will be converted into steam ; at points nearer to the flame the quicker 

 it will be vaporized until a position is reached where the drop instead of being 

 vaporized rolls about on the plate. This point Rubinstein calls the " spheroidal 

 zone " and the point of optimum temperature for fixing dry blood films. The 

 preparations are to be placed blood side down on this zone so that an edge of 



