BLOOD. 7 



other crystals derivatives of haemoglobin may also be obtained from blood. Of these (6), 

 Haemin (Hydrochlorate of Haematin), or Teichmann's Crystals, are of most importance, as their 

 presence is considered one of the surest as well as one of the most delicate tests for blood 

 in medico-legal cases. 



PREPARATION. Take a drop of blood from the finger and allow it to dry on a slide, or 

 take some powdered dried blood previously prepared and add to it a trace of finely powdered 

 common salt. Moisten the whole with a drop of glacial acetic acid, apply a cover, and heat 

 the slide gently over the flame of a spirit lamp till bubbles of gas appear. Allow the prepara- 

 tion to cool, and apply a cover-glass. 



EXAMINATION. (H.) Observe the short reddish-brown prismatic crystals scattered all 

 over the field ; they are best seen where they are attached to small masses of blood. These 

 are the crystals of Hsemin. These make good permanent preparations. To preserve them, 

 take off the cover-glass, and remove the surplus acid with blotting paper. Add a drop of 

 Farrant's solution, re-apply the cover. For the method of sealing up the preparation per- 

 manently, see p. xlix. 



For the method of ascertaining the number of coloured blood-corpuscles by Malassez's 

 method, see Archives de Physiologic, 1874, or the Practitioner, July 1878, where Dr. Cowers 

 describes the haemacytometer. The amount of haemoglobin may be ascertained by means of 

 the haimaglobinometer. See Clinical Society's Transactions, vol. xii., p. 64. 



UNIVERSITY 



