36 FORMATION OF BED CORPUSCLES. [BOOK i. 



continuing to exist after having lost their hemoglobin, must 

 therefore entail a daily destruction of many red corpuscles. 



Even in health then a number of red corpuscles must be 

 continually disappearing; and in disease the rapid and great 

 diminution which may take place in the number of red corpuscles 

 shews that large destruction may occur. 



We cannot at present accurately trace out the steps of this 

 disappearance of red corpuscles. In the spleen pulp, red corpuscles 

 have been seen in various stages of disorganisation, some of them 

 lying within the substance of large colourless corpuscles, and as it 

 were being eaten by them. There is also evidence that destruction 

 takes place in the liver itself, and indeed elsewhere. But the 

 subject has not yet been adequately worked out. 



27. This destruction of red corpuscles necessitates the birth 

 of new corpuscles, to keep up the normal supply of hemoglobin ; 

 and indeed the cases in which after even great loss of blood by 

 hemorrhage a healthy ruddiness returns, and that often rapidly, 

 shewing that the lost corpuscles have been replaced, as well as 

 the cases of recovery from the disease anaemia, prove that red 

 corpuscles are, even in adult life, born somewhere in the body. 



In the developing embryo of the mammal the red corpuscles of 

 the blood are not hemoglobin-holding non-nucleated discs of stroma, 

 but coloured nucleated cells which have arisen in the following way. 



In certain regions of the embryo there are formed nests of 

 nuclei imbedded in that kind of material of which we have already 

 (5) spoken, and of which we shall have again to speak as un- 

 differentiated protoplasm. The special features of this undifferen- 

 tiated protoplasm are due to the manner in which its living basis 

 ( 5), in carrying on its continued building up and breaking down, 

 disposes of itself, its food, and its products. These are for a while 

 so arranged as to form a colourless mass with minute colourless 

 solid particles or colourless vacuoles imbedded in it, the whole 

 having a granular appearance. After a while this granular looking 

 protoplasm is in large measure gradually replaced by material of 

 different optical and chemical characters, being for instance more 

 homogeneous and less "granular "in appearance; this new material 

 is stroma, and as it is formed, there is formed with it and in some 

 way or other held by it a colouring matter, hemoglobin. We 

 cannot at present say anything definite as to the way in which and 

 the steps by which the original protoplasm is thus to a large 

 extent differentiated into stroma and hemoglobin. All we know 

 is that the existence of what we have called living substance is 

 necessary to the formation of stroma and hemoglobin. We there- 

 fore seem justified in speaking of this living substance as manu- 

 facturing these substances, but we do not know whether the living 

 substance turns itself so to speak into stroma or hemoglobin or 

 both, or whether by some agency, the nature of which is at present 

 unknown to us, it converts some of the material which is present in 



