32 STRUCTURE OF RED CORPUSCLE. [BOOK i. 



When laky blood is allowed to stand a sediment is formed (and 

 may be separated by the centrifugal machine) which on exami- 

 nation is found to consist of discs, or fragments of discs, of a 

 colourless substance exhibiting under high powers an obscurely 

 spongy or reticular structure. These colourless thin discs seen 

 flat-wise often appear as mere rings. The substance composing 

 them stains with various reagents and may thus be made more 

 evident. 



The red corpuscle then consists obviously of a colourless frame- 

 work, with which in normal conditions a red colouring matter is 

 associated ; but by various means the colouring matter may be 

 driven from the framework and dissolved in the serum. 



The framework is spoken of as stroma ; it is a modified or 

 differentiated protoplasm, and upon chemical analysis yields a pro- 

 teid substance belonging to the globulin group, and other matters, 

 among which is the peculiar complex fat called lecithin, of which 

 we shall have to speak in treating of nervous tissue. 



The red colouring matter which in normal conditions is asso- 

 ciated with this stroma may by appropriate means be isolated, and, 

 in the case of the blood of many animals, obtained in a crystalline 

 form. It is called Haemoglobin, and may by proper methods be 

 split up into a proteid belonging to the globulin group, and into a 

 coloured pigment, containing iron, called Hcematin. Haemoglobin 

 is therefore a very complex body. It is found to have remarkable 

 relations to oxygen, and indeed as we shall see the red corpuscles 

 by virtue of their haemoglobin have a special work in respiration ; 

 they carry oxygen from the lungs to the several tissues. We 

 shall therefore defer the further study of haemoglobin until we 

 have to deal with respiration. 



Though the haemoglobin, as is seen in laky blood, is readily 

 soluble in serum (and it is also soluble in plasma), in the intact 

 normal blood it remains confined to the corpuscle ; obviously 

 there is some special connection between the stroma and the he- 

 moglobin ; it is not until the stroma is altered, we may perhaps 

 say killed (as by repeated freezing and thawing), that it loses its 

 hold on the haemoglobin, which thus set free passes into solution 

 in the serum. The disc of stroma when separated from the haemo- 

 globin has as we have just said an obscurely spongy texture ; but 

 we do not know accurately the exact condition of the stroma in 

 the intact corpuscle or how it holds the haemoglobin. There is 

 certainly no definite membrane or envelope to the corpuscle, for 

 by exposing blood to a high temperature, 60 C., .the corpuscle 

 will break up into more or less spherical pieces, each still consisting 

 of stroma and haemoglobin. 



The quantity of stroma necessary to hold a quantity of haemo- 

 globin is exceedingly small. Of the total solid matter of a 

 corpuscle more than 90 p. c. is haemoglobin. A red corpuscle in 

 fact is a quantity of haemoglobin held together in the form of a 



