436 BLOOD AND LYMPH. 



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. The length of life of a red corpuscle in the circula- 

 tion has been investigated in various ways, but the conclusions 

 reached have not been uniform. Estimates vary from two to four 

 weeks* or more. 



Just when and how the corpuscles go to pieces is not definitely 

 known. The natural supposition would be that the more aged 

 corpuscles, on account of diminished resistance, undergo hemolysis 

 while in the blood-stream. But actual demonstration of such a 

 procedure has not been furnished. Other views have been pro- 

 posed. It has been suggested that their destruction takes place 

 in the spleen or lymph-glands or in the liver by the process of 

 phagocytosis (p. 441). Certain large cells (macrophags) have 

 been described in the spleen which, at times, contain red blood- 

 corpuscles or fragments of them in their cytoplasm. In the bird 

 and some other animals Kyesf has been able to demonstrate that 

 the so-called Kupffer cells of the liver actually ingest red corpus- 

 cles, and subsequently digest them so as to hberate the iron of 

 the hemoglobin in a form that can be detected by microchemical 

 reactions. These Kupffer cells are modified or specialized endo- 

 thelial cells of the venous capillaries of the liver, and the cells in 

 the spleen which have the same property seem to be of the same 

 type. Kyes proposes for them the name hemophags. The large 

 number of these cells present in the liver, and their action in de- 

 stroying the red corpuscles and liberating the iron falls in with 

 the known function of the liver in producing an iron-free bile- 

 pigment from the hematin. The extent to which this process 

 occurs seems to vary in different animals, | but certainly it is not 

 the sole method employed in the body. Another possibility that 

 has been brought forward is the method of fragmentation. In 

 this process the corpuscles break into smaller and smaller pieces 

 until they are reduced to a fine powder. Fragments of this char- 

 a,cter may be found in the blood or spleen, but nothing is known 

 as to the immediate cause of the process, nor has it been deter- 

 mined how generally it occurs. The continual destruction of red 

 corpuscles imphes, of course, a continual formation of new ones. 

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

 the production of red corpuscles is the red marrow of bones. 

 In this tissue hematopoiesis, as the process of formation of red 

 corpuscles is termed, goes on continually, the process being much 

 increased after hemorrhages and in certain pathological condi- 



* Ashby, "Journal of Exp. Med.," 29, 267, 1919. 



t Kyes, "Internationalen Monatsschrift f. Anat. u. Physiol.," 31, 543, 1914. 



t Rous and Robertson, "Journal of Exp. Med.," 25, 651, 1917. 



