70 HOWELL. [Vol. IV. 



views. I shall not attempt to make the review as complete as 

 the material which I have accumulated might enable me to do, 

 since some of the work published does not need special men- 

 tion. I have added, however, an appendix, giving the complete 

 list of articles which I have been able to consult. 



Before 1869 it was quite generally believed that the red 

 corpuscles are formed from the white corpuscles, most probably 

 while in the circulation. This theory found its way into the 

 text-books, and, to a certain extent is still advocated by some 

 histologists. In fact, some of the most recent investigations 

 favor this view, although the evidence is so overwhelmingly 

 against it. 



Feuerstack (17) in a recent series of observations, made 

 upon animals with nucleated red corpuscles, describes in the 

 circulation transitional forms between the white and the red 

 corpuscles. The colorless cell from which the other forms are 

 derived has a relatively large nucleus and small cell body. 

 The cell substance increases while the nucleus becomes smaller, 

 and not unfrequently takes a peripheral position. Haemoglobin 

 develops in the cell, which gradually changes in shape from a 

 spherical to an oval form. Most of the transitional stages are 

 found in the bone marrow and spleen, though in these organs 

 they occur not in the parenchyma, but within the blood-vessels. 

 Feuerstack gives no sections to show how these developing 

 corpuscles are placed within the blood-vessels of the marrow 

 and spleen. When he says that the red corpuscles are derived 

 from white corpuscles, he differs somewhat from the older 

 observers, who thought that the white corpuscles might change 

 to red anywhere in the circulation, — were, indeed, continually 

 undergoing such a change, — while Feuerstack limits it to the 

 blood-vessels of the marrow and spleen. On the other hand, 

 his conclusions, if not taken too literally, agree very well with 

 some new views of Denys upon the formation of red corpuscles 

 in the marrow of birds. While the older observers accepted 

 this view of the origin of the red corpuscles without much 

 question, no one was able to obtain satisfactorily the transi- 

 tional forms, so that Kolliker (3) was forced to say that the 

 question was still undecided. Erb (4) asserted, however, that 

 he was able to get transitional forms in the circulation by 

 means of a certain method of treatment. Blood after treat- 



