64 PRACTICAL PHYSIOLOGY. [VII 



The blood, therefore, contains 61.1 haemoglobin. The following table givea 

 the proportion of haemoglobin, the normal amount of haemoglobin being taken 



known volume of water, whereby the haemoglobin is dissolved out of the red 

 corpuscles and the fluid becomes transparent. The quantity of haemoglobin is 

 calculated from the thickness of the stratum of fluid required to correspond 

 exactly to the colour-intensity of a coloured glass accompanying the instru- 

 ment. The latter is coloured of a tint similar to a solution of haemoglobin, 

 and is fixed to the instrument by means of a suitable brass fixture. 



1. Fix the coloured glass with its brass frame in the instrument. 



2. Mix 10 c.mm. blood with .5 cc. distilled water. In a few seconds a trans- 

 parent solution of haemoglobin is obtained. 



3. Pour this solution into the reservoir (r), and rotate the inner tube so 

 that the fluid passes between the two glasses. Direct the instrument towards 

 a white light or the sky, not towards the sun, and compare the colour of the 

 solution with the standard coloured glass, a procedure which is facilitated by 

 placing a milky glass between the source of light and the layer of blood, so as 

 to obtain diffuse white light. When the two colours appear to have as near 

 as possible the same intensity, read off" on the scale the thickness of the layer 

 of blood, and from this, by means of the accompanying table, ascertain the 

 corresponding amount of haemoglobin. 



This is done in the same way as tor the cytometer, but the graduation is 

 difi'erent, as in the one case we have to do with a candle-flame, and in the 

 other with a coloured glass. 



In very pronounced cases of anaemia, even with a layer of blood 6 mm. in 

 thickness, owing to the limits of the instrument, the intensity of the mixture 

 of blood may be less than that of the coloured glass. In such a case, 

 instead of 10 c.mm. of blood, use 20 c.mm. 



Graduation of the Cliromometer. — As the coloured glass has not absolutely 

 the same intensity of colour in all chromometers, one must first of all estimate 

 the colour-intensity of the glass itself. This is most easily done by ascertain- 

 ing in a given specimen of blood what degree ot the chromometer corresponds 

 to the scale of the cytometer of the same blood. 



Suppose that a specimen of blood by means of the cytometer gave no, and 

 by the chromometer 140 ; the number 1 10 of the cytometer = 100 haemoglobin, 

 so that the chromometer number 140 must also be = 100. "With the aid of 

 the formula (p. 63) a similar table can be constructed for the chromometer. 

 Suppose the blood investigated = 280 ; then by the aid >f the formula and 

 the data from normal blood we have— 



14,000^^ 



280 280 



This blood, therefore, contains 50 parts of haemoglobin. 



Example. — Blood gives 130 with the cytometer and 190 with the chromo 

 meter ; what is the initial number of the chromometer graduation correspond 

 ing to icx) parts of haemoglobin ! 



