THE COLOURED BLOOD-CORPUSCLES. 27 



18. Preparation of Fibrin-ferment. It must be kept in stock. 

 Precipitate blood-serum with a large excess of alcohol, collect the 

 copious precipitate ; cover it with absolute alcohol, and allow it 

 to stand at least a month the longer the better. Dry the pre- 

 cipitate at 35C., and afterwards over sulphuric acid. Keep it as 

 a dry powder in a well-stoppered bottle. When a solution is 

 required, extract some of the dry powder with 100 volumes of 

 water ; filter. The filtrate contains the ferment. 



LESSON IV. 



THE COLOURED BLOOD-CORPUSCLES. 

 SPECTRA OF HAEMOGLOBIN AND ITS COMPOUNDS. 



Enumeration of the Corpuscles. Several forms of instruments 

 are in use, e.g., those of Malassez, Zeiss, and Gowers. 



1. The Haemocytometer of Gowers' consist of 



(a.) A small pipette, which, when filled to the mark on 

 its stem, holds 995 c.mm. (Fig. 2, A). 



(6.) A capillary tube to hold 5 c.mm. (B). 



(c.) A small glass jar in which the blood is diluted (D). 



(d.) A glass stirring rod (E). 



(e). Fixed to a brass plate a cell \ of a millimetre deep, 

 and with its floor divided into squares ^ mm., in which 

 the blood-corpuscles are counted. 



(/.) The diluting solution consists of a solution of sodic 

 sulphate in distilled water specific gravity, 1025. 



This instrument can be used with any microscope. 



2. Mode of using the Instrument. 



(a.) By means of the pipette (A) place 995 c.mm. of the 

 diluting solution in the mixing jar (D). 



