THE CIRCULATING LIQUIDS OF THE BODY 51 



crystallizes in the form of small rhombic plates, of a brownish or 

 brownish- black colour. They are insoluble in water, but readily 

 soluble in dilute alkalies (see Practical Exercises, p. 66). 



Chemistry of the White Blood Corpuscles. The composition of 

 pus-cells and the leucocytes of lymphatic glands has alone been 

 investigated. The chief constituents of the latter are a globulin 

 coagulating by heat at 48 to 50 C. ; a nucleo-proteid coagulating in 

 5 per cent, magnesium sulphate solution at 75 C., and causing 

 coagulation of the blood on injection into the veins of rabbits ; an 

 albumin coagulating at 73 C. ; and a ferment with powers like the 

 pepsin of the gastric juice. In pus-cells glycogen has been found. 



The Quantity of Blood. The quantity of blood in an animal 

 is best determined by the method of Welcker. The animal 

 is bled from the carotid into a weighed flask. When blood 



FIG. ii. DIAGRAM TO ILLUSTRATE THE DISTRIBUTION OF THE BLOOD IN 



THE VARIOUS ORGANS OF A RABBIT (AFTER RANKE'S MEASUREMENTS). 



The numbers are percentages of the total blood. 



has ceased to flow, the vessels are washed out with water 

 or normal saline solution, and the last traces of blood are 

 removed by chopping up the body, after the intestinal 

 contents have been cleared away, and extracting it with 

 water. The extract and washings are mixed and weighed ; 

 a given quantity of the mixture is placed in a haematino- 

 meter (a glass trough with parallel sides, e.g.), and a weighed 

 quantity of the unmixed blood diluted in a similar vessel 

 till the tint is the same in both. From the amount of 

 dilution required, the quantity of blood in the watery solu- 

 tion can be calculated. This is added to the amount of 

 unmixed blood directly determined. 



Many other methods have been devised on the principle 

 of injecting a known quantity of some substance into the 

 circulating blood, aiid then, after an interval has been 

 allowed for mixture, determining the change produced in a 



42 



