ORIGIN OF THE RED BLOOD-CORPUSCLES. 15 



period of development blood-corpuscles are formed within other large cells of the 

 mesoblast, and that part of the protoplasm of these blood-forming cells remains to 

 form the wall of the future blood-vessel. 



(C.) Later Formation of Bed Blood-Corpuscles. There is much 

 diversity of opinion as to how coloured blood-corpuscles are formed in 

 mammals at a later period. [They have been described as derived from 

 colourless corpuscles, one set of observers (including Kolliker) main- 

 taining that the nucleus of these corpuscles disappears, while the 

 peri-nuclear portion remains, becomes flattened and coloured, and 

 assumes the characters of the mammalian blood-corpuscles. On the 

 other hand, other observers (including Wharton Jones, Gulliver, Busk, 

 Huxley, and Balfour) are of opinion that the nucleus becomes pigmented, 

 and forms the future blood-corpuscle. It is still doubtful, however, 

 whether coloured corpuscles are developed in either of these ways.] 

 Neumann and Bizzozero described peculiar corpuscles occurring in the 

 red marrow of bone, which they maintain become developed into 

 coloured blood-corpuscles, undergoing a series of changes, and forming 

 a series of intermediate forms, which may be detected in the red 

 marrow. Bizzozero holds that it is the nucleus of the marrow-cell 

 which is coloured, while Neumann thinks it is the perinuclear part 

 which becomes coloured, and forms the blood-corpuscle. Schafer's 

 observations on the red marrow of the guinea-pig rather tend to con- 

 firm Neumann's view. 



These transition cells are said by Erb to be more numerous after 

 severe haemorrhage, the number of them occurring in the blood 

 corresponding with the energy -of the formative process. In dogs 

 and guinea-pigs which he had rendered anaemic, Bizzozero found in the 

 marrow and spleen nucleated red blood-corpuscles, which increased by 

 division. 



According to Neumann, the bone-marrow of adults contains all transi- 

 tion forms, from nucleated coloured corpuscles to true red blood- 

 corpuscles. After copious haemorrhage, these transition forms appear 

 in numbers in the blood-stream. 



Red or blood-forming marrow occurs in the bones of the skull, and in most of the 

 bones of the trunk, while the bones of the extremities either contain yellow 

 marrow (which is essentially fatty in its nature), or, at most, it is only the heads 

 of the long bones that contain red marrow. Where the blood regeneration process 

 is very active, however, the yellow marrow may be changed into red, even through- 

 out all the bones of the extremities (Neumann). 



Rindfleisch also regards the connective substance of the red marrow and the 

 spleen as the mother-tissue of the red blood-corpuscles, the connective substance 

 or the hsematogenous connective tissue either temporarily or permanently forming 

 red blood-corpuscles. Once the red corpuscles are formed, they easily enter the 

 blood-stream, as the capillaries and veins of the red marrow have either no walls 



