7 8 HOWELL. [Vol. IV. 



or, as a third possibility, the erythroblasts are carried to the 

 marrow and there undergo the final changes. The nucleated 

 red corpuscles pass into the usual red corpuscles by a loss of 

 the nucleus. This, he thinks, occurs in the way described by 

 Kolliker and by Neumann ; that is, by disintegration and 

 absorption within the cell. In his latest paper Lowit describes 

 some new and rather remarkable observations upon the erythro- 

 blasts. He finds that he can obtain erythroblasts easily from 

 the veins which bring back blood from the blood-forming 

 organs ; while in the superior vena cava they occur rarely, 

 and in the left heart and arterial system they are entirely 

 wanting. Though few erythroblasts are found in the superior 

 cava and right heart, nevertheless blood from these portions of 

 the vascular system, when treated for a number of hours with 

 a modified Pacini's liquid, shows a considerable number of red 

 corpuscles which contain a granular body of the shape and 

 general appearance of a nucleus. The granules may be few 

 or many, and in some cases they are connected by a sort of 

 nuclear network. Lowit's description corresponds very well 

 to the "transitional forms" of Erb which have already been 

 mentioned. He interprets these structures as erythroblasts in 

 which the nucleus is disappearing. Apparently, then, he be- 

 lieves that an erythroblast may develop its haemoglobin and 

 lose its nucleus by absorption while in the venous blood and 

 during the time required for that blood to flow from the blood- 

 forming or2:an to the left heart. The blood that flows from 

 the lungs to the left heart must contain, therefore, a number of 

 newly formed corpuscles. Nevertheless, comparisons made be- 

 tween the blood of the left and the right heart showed that the 

 former contained fewer "corpuscles and less haemoglobin than 

 the latter. Hence, during the passage of the blood through 

 the lungs there must occur also a more or less important de- 

 struction of red corpuscles. 



It has been generally believed that in the marrow the 

 nucleated red corpuscles are not arranged in any definite way, 

 but are mingled indiscriminately with the other elements of the 

 marrow. Denys (14) in a recent very interesting paper states 

 that this is not the case, at least not in the marrow of the 

 bird. He accepts the terms erythroblast and leucoblast pro- 

 posed by Lowit, and states that in sections of the marrow 



