78 THE CIRCULATING LIQUIDS OF THE BODY 



head T move the tinted wedge K till the depth of colour is the same 

 in the two compartments. The percentage of the normal quantity 

 of haemoglobin is given by the graduated scale P. For example, if the 

 reading is 90, the blood contains 90 per cent, of the normal amount; 

 if 100, it contains the normal quantity. The observations should be 

 made in a dark room, the white surface S, arranged below the compart- 

 ments a and a', being illuminated by a lamp. Or the instrument may 

 be placed in a small box, lighted by a candle. It is best that each result 

 should be the mean of two readings, one just too large and the other 

 just too small. In any case the instrument does not give readings 

 accurate to less than 5 per cent. 



(c) Hoppe-Seyler's Method. Two parallel-sided glass troughs are 

 used. In one is put a standard solution of oxy haemoglobin of known 

 strength, in the other a measured quantity of the blood to be 



tested. The latter is diluted 



K 



with water until its tint 

 appears the same as that 

 of the standard solution, 

 when the troughs are placed 



Fig. 23. Fleischl's Hasmometer. 



Fig. 24. Crystals of Hamin 

 (Frey). 



side by side on white paper. 

 From the quantity of water 

 added it is easy to calculate 

 the proportion of haemo- 

 globin in the undiluted 



blood. Greater accuracy is obtained if the haemoglobin in the standard 

 solution and that of the blood are converted into carbonic oxide haemo- 

 globin by passing a stream of coal-gas through them. 



(d) Tallquist's Method. In this method the tint produced by a 

 drop of blood on a piece of white filter-paper is compared with a scale 

 representing 10 percentages of haemoglobin (from 10 to 100 per cent.). 

 The standard filter-paper is supplied in the form of a book with the 

 scale. To make an estimation, all that is necessary is to touch a drop 

 of blood with a piece of the filter-paper, and allow the blood to diffuse 

 slowly through the paper, so as to give an even stain. The position 

 of the stain is then determined by the scale; e.g., it may be deeper 

 than 90, but fainter than 100, in which case the percentage of haemo- 

 globin lies between 90 and 100. The method is by no means a very 

 accurateone, but more accurate than it appears at first sight. 



(5) Microscopic Test for Blood-Pigment. Put a drop of blood on a 

 slide. Allow the blood to dry, or heat it gently over a flame, so as to 

 evaporate the water. Add a drop of glacial acetic acid ; put on a cover- 



