xiv THE LYMPH 539 



products elaborated in the giant cells. But from the very im- 

 portant fact discovered by van der Stricht to the effect that in a 

 case of progressive pernicious anaemia there was complete absence 

 of giant cells in the bone marrow, it may be assumed that they 

 are useful to the production of erythrocytes. 



The simultaneous presence in bone marrow of erythroblasts 

 (nucleated embryonic red corpuscles) and erythrocytes (adult red 

 corpuscles with no visible nuclei) shows beyond doubt that it 

 is the seat of an active formation of the latter which are 

 found in the blood in large numbers. After repeated bleeding the 

 haematopoietic function of the bone marrow is conspicuously 

 increased. The number of haematoblasts undergoing mitotic 

 division increases; even that part of the marrow of the long 

 bones which is normally inactive assumes a haematopoietic function 

 (Orth, Litten, Foa and Pellacani, Bizzozero and Salvioli). Under 

 these conditions a large number of nucleated red corpuscles enter 

 the circulatory torrent (Erb). 



Alterations in bone marrow can also be observed in many 

 diseases in which there is marked alteration of the corpuscles 

 (leucaemia, pernicious anaemia, typhoid, smallpox). 



According to Danilewski and Selenski the subcutaneous or 

 intraperitoneal injection of watery extracts of bone and splenic 

 marrow produces a considerable increase in the number of 

 erythrocytes (up to 50 per cent) and the haemaglobin content 

 (up to 40 per cent) of the blood of rabbits and dogs. This effect 

 was confirmed by Fowler in regard to extract of bone marrow. 



It was formerly admitted (Bizzozero), and is still retained by 

 some authors (Paladino), that erythrocytes arise from direct 

 transformation of leucocytes. This theory, for which there is 

 no experimental evidence, is now being given up. The only 

 well-established fact is that the erythrocytes increase by mitotic 

 division. 



On the other hand it is certain that adult erythrocytes are 

 derived from embryonic haematoblasts. The blood of the human 

 foetus at the fourth month contains only nucleated red corpuscles ; 

 at the end of the ninth month these have become very rare. 

 After that they are completely replaced by erythrocytes with no 

 perceptible nucleus. How does the disappearance of the embryonic 

 nucleus of the mammalian erythrocyte come about ? Eindfleisch 

 asserts that there is active extrusion of the nucleus ; the haemato- 

 blast is deformed into the shape of a bell or watch-glass, the 

 vertex of which, containing the nucleus, is finally disrupted. The 

 bi-concavity of the erythrocytes is a vestige of this enucleation, 

 which may be regarded as a kind of autocastration. The majority 

 of observers hold more simply that the embryonic nucleus 

 atrophies gradually, and ends by disappearing. If, however, this 

 view were well founded we ought to find a number of transitional 



