926 PHYSIOLOGY 



be a great preponderance of sodium chloride in the supernatant fluid. 

 If a 1 or 2 per cent, solution of urea in water be added to defibrinated 

 blood, the corpuscles will swell up and burst just as if distilled water 

 had been added. There are a large number of substances to which 

 the corpuscles are permeable, e.g. alcohol, chloroform, ether, &c. In 

 their permeability the corpuscles resemble most other vegetable and 

 animal cells in permitting the passage of all those substances which 

 are soluble in fats and the allied substances, cholesterin, lecithin, and 

 protagon, which are invariable constituents of all living cells. Accord- 

 ing to Overton the external limiting pellicle of the red corpuscles, as 

 in most living cells, is formed by a lecithin-cholesterin compound, 

 whose solvent power determines the permeability of the cell by foreign 

 substances. If therefore we wish to stain the living cell we must 

 choose some dyestuff, such as methylene blue or neutral red, which is 

 soluble in such lipoid bodies. 



CHEMISTRY OF THE RED BLOOD-CORPUSCLES 



The red corpuscles consist of two parts, hemoglobin and stroma, 

 probably in a state of loose chemical combination. By various means 

 it is possible to destroy this combination and to dissolve out the 

 haemoglobin, leaving the colourless swollen-up stroma floating in the 

 plasma. At the same time the blood becomes darker but more 

 transparent, and is spoken of as ' laked ' blood. 



It has been thought by Schwann, Schafer, and others that the red corpuscle 

 consists of a solution of haemoglobin contained within an envelope which contains 

 lecithin and cholesterin and forms the stroma. Though the haemoglobin can 

 be separated from the stroma by very simple means, it is difficult to believe 

 that it is in watery solution. Thus the blood-corpuscles contain a greater 

 percentage of solids than any- soft tissue of the body. The blood-cor- 

 puscles contain 36-7 per cent, solids, as against muscular tissue with 25 per 

 cent, or nervous with 22 per cent, solids. Of these solids, 95 per cent, 

 consist of haemoglobin, so that the solution would have to contain at least 

 30 per cent, haemoglobin. No solution of haemoglobin of this strength can be 

 prepared. In many animals, such as the rat and guinea-pig, it is sufficient 

 merely to 'lake' the blood, i.e. to bring the haemoglobin into solution with the 

 surrounding plasma or serum, in order to make the haemoglobin crystallise out. 

 Some form of combination is therefore necessary in corpuscles if merely to 

 keep the haemoglobin from separating out in a crystalline form. 



Blood may be ' laked ' by any of the following means : 



(a) Addition of a small amount of ether. 



(b) Free dilution with water. 



(c) Alternate freezing and thawing of the blood. 



(d) Addition of bile-salts. 



(e) The action of foreign blood-serum or of various haemolysins 

 whose nature we shall have to discuss later. 



