BLOOD. 



343 



Bile-pigments and Urinary Pigments Haemoglobin is regarded as the 

 parent-substance of the bile-pigments and the urinary pigments. 



Origin and Fate of the Red Corpuscles. The mammalian red corpuscle 

 is a cell that has lost its nucleus. It is not probable, therefore, that any given 

 corpuscle lives for a great while in the circulation. This is made more certain 

 by the fact that haemoglobin is the mother-substance from which the bile- 

 pigments are made, and, as these pigments are being excreted continually, it is 

 fair to suppose that red corpuscles are as steadily undergoing disintegration in 

 the blood-stream. Just how long is the average life of the corpuscles has not 

 been determined, nor is it certain where and how they go to pieces. It has 

 been suggested that their destruction takes place in the spleen, but the observa- 

 tions advanced in support of this hypothesis are not very numerous or con- 

 clusive. Among the reasons given for assuming that the spleen is especially 

 concerned in the destruction of red corpuscles, the most weighty is the histo- 

 logical fact that one can sometimes find in teased preparations of spleen-tissue 

 certain large cells which contain red corpuscles in their cell-substance in various 

 stages of disintegration. It has been supposed that the large cells actually 

 ingest the red corpuscles, selecting those, presumably, which are in a state of 

 physiological decline. Against this idea a number of objections may be 

 raised. Large leucocytes with red corpuscles in their interior are not found 

 so frequently nor so constantly in the spleen as we would expect should be 

 the case if the act of ingestion were constantly going on. There is some 

 reason for believing, indeed, that the whole act of ingestion may be a post- 

 mortem phenomenon ; that is, after the cessation of the blood-stream the 

 amoeboid movements of the large leucocytes continue, while the red corpuscles 

 lie at rest conditions which are favorable to the act of ingestion. It may be 

 added also that the blood of the splenic vein contains no haemoglobin in solu- 

 tion, indicating that no considerable dissolution of red corpuscles is taking 

 place in the spleen. Moreover, complete extirpation of the spleen does not 

 seem to lessen materially the normal destruction of red corpuscles, if we may 

 measure the extent of that normal destruction by the quantity of bile-pigment 

 formed in the liver, remembering that haemoglobin is the mother-substance 

 from which the bile-pigments are derived. It is more probable that there is 

 no special organ or tissue charged with the function of destroying red corpus- 

 cles, and that they undergo disintegration and dissolution while in the blood- 

 stream and in any part of the circulation, the liberated haemoglobin being 

 carried to the liver and excreted in part as bile-pigment. The continual 

 destruction of red corpuscles implies, of course, a continual formation of new 

 ones. It has been shown satisfactorily that in the adult the organ for the 

 reproduction of red corpuscles is the red marrow of bones. In this tissue 

 hcematopoiesis, as the process of formation of red corpuscles is termed, goes on 

 continually, the process being much increased after hemorrhages and in certain 

 pathological conditions. The details of the histological changes will be found 

 in the text-books of histology. It is sufficient here to state simply that a 

 group of nucleated colorless cells, erythroblasts, is found in the red marrow. 



