iv THE BLOOD: FOEMED 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 6.0,540 grrns., 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-intestinal 



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, ;/: 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 </) ; 

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

 equation : 



a + c : a : : d : x 



axd 

 and therefore x = 



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 .< : 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 Jy of the body- 

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

 kilograms body-weight. 



VOL. i H a 



