820 PHYSIOLOGY 



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, haemoglobin 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 con- 

 sists 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-corpuscles 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 in the surrounding plasma or serum, 

 in order to make the haemoglobin crystallise out. Some form of combination is there- 

 fore necessary in the 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. 

 (6) 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 hsemolysins whose 

 nature we shall have to discuss later. 



From such laked blood we may prepare either haemoglobin or stroma. 



In order to separate the stroma from the haemoglobin, blood which has been de- 

 fibrinated or prevented from clotting by the addition of a little sodium oxalate is 

 centrifuged until all the formed elements form a solid cake at the bottom of the tube. 

 The tube is then filled up with normal saline fluid and again centrifuged, and this 

 process repeated twice in order to wash away adherent plasma or serum. After the 

 final washing two volumes of distilled water saturated with ether are added to one 

 volume of caked corpuscles. The corpuscles swell up and their haemoglobin passes 

 into solution into the surrounding fluid. The blood is laked. The fluid is once more 

 centrifuged in order to throw down white blood corpuscles. A 1 per cent, solution 

 of acid sodium sulphate is now added drop by drop until the solution acquires the 

 opaque appearance presented by ordinary blood. The action of this salt, as of dilute 

 acids, is to precipitate the swollen-up stromata, which reacquire the power of reflecting 

 light from their surfaces and restore the opacity to the blood. On centrifuging, the 

 stromata are thrown down, and can be collected and washed with distilled water several 

 times on the centrifuge. 



