iv THE BLOOD: FOKMEI) CONSTITUENTS 99 



the fixed constituents of the blood remaining in the system, but 

 also such as have penetrated by the lymphatic system and by 

 diffusion from the tissues, during and soon after the bleeding. 

 In one of the criminals, who weighed 60,540 grins., the mass of 

 the blood weighed 7520 grins., i.e. one-eighth of the body-weight. 

 More exact results were obtained with the chromometric 

 method, which is based on the colouring properties of the blood 

 pigment (haemoglobin). It was first employed by Welcker (1854) 

 and was perfected later by Gscheidlen (1873). A little normal 

 blood is first drawn from the animal and weighed ; the whole of 

 the blood that can be extracted by bleeding is then collected ; 

 that left behind is subsequently washed out of the system by 

 irrigating with a stream of isotonic (0*60-0 '55 per cent) salt 

 solution ; then, after removing the contents of the gastro-iutestinal 

 canal, gall bladder and urinary bladder, the viscera are minced up 

 and soaked for several hours in the saline fluid used for washing ; 

 lastly, the washings are mixed with the mass of blood obtained 

 by bleeding. The blood-content is calculated from the coloured 

 liquid obtained, after determining the quantity of saline that 

 must be added to the weighed specimen of blood in order to obtain 

 the same degree of colour. To make the experiment more exact 

 it is advisable to saturate the haemoglobin with carbon monoxide, 

 in order to secure the same degree of colour in both mixtures. 



The calculation for determining the quantity of blood contained in the 

 body is very simple : If a is the quantity of blood extracted in the first 

 bleeding, x the quantity of blood left in the body, b the quantity of physio- 

 logical saline employed to wash out the vascular system and organs of the 

 animal, c the quantity of physiological saline necessary, to make the colour 

 of the blood a equal to that of the blood x, plus the fluid b (a quantity which 

 is known to us, and which we may, to simplify matters, denote as d) ;. 

 it is easy to calculate the quantity of blood x according to the following 

 equation : 



a 4- c : a : : d : x 



and therefore x-= a 



a + c 



Having thus determined the value x, we can at once arrive at the total 

 volume of the blood by adding the first portion a extracted in the pre- 

 liminary bleeding to x : if we then multiply the volume of blood by its 

 specific weight, we obtain the absolute weight of blood, the relation of which 

 to the total body-weight of the animal has finally to be calculated. 



Welcker came to the conclusion that the mass of the blood 

 varies in dogs from 7 to 9 per cent of the body-weight, in rabbits 

 from 5 to 9 per cent. Bischoff (1855), who applied these methods 

 to the bodies of two criminals, obtained results which approxi- 

 mated closely to those obtained by Welcker for dogs (7*1 to 7'7 per 

 cent). Assuming that in man the blood averages ^ of the body- 

 weight, there would be 5 kilograms of blood in an individual of 65 

 kilograms body- weight. 



VOL. I H a 



