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HOWELL. [Vol. IV. 



elongated strap shape, and may be bent into a horseshoe, or 

 may be coiled upon itself one or more times, like the leucocytes 

 found so abundantly in the cat's blood. These cells, are, how- 

 ever, larger than leucocytes; and it is probable that they 

 belong to the same class as the ordinary marrow cells (Fig. 

 \2, c and d). 



4. Some of the ordinary marrow cells have their protoplasm 

 loaded down with coarse granules which stain readily with 

 eosin, methyl green, etc. (Fig. 12, e and t). Sometimes these 

 cells are very numerous : they evidently play some important 

 part in the metabolic changes going on in the marrow. They 

 do not appear to be confined to the marrow, since Heidentain 

 has described what seems to be the same cell in the lymphoid 

 tissue of the intestine, though he was unable to arrive at any 

 satisfactory conclusions as to its function. 



6. The so-called giant cells. In the red marrow of grown 

 animals these are always of the kind described by Bizzozero 

 as giant cells with budding nuclei to distinguish them from the 

 multinucleated giant cell, or myeloplaque, found in develop- 

 ing bone, in pathological formations, etc. A more detailed 

 description of these cells with a discussion of their functions 

 is given in an accompanying paper. 



7. Free nuclei are found sometimes in considerable numbers. 

 In size and in the way in which they stain, they resemble 

 exactly the nuclei of the matured nucleated red corpuscles, 

 and there can be but little doubt that they arise from these 

 cells. 



With reference now to the origin of the nucleated red cor- 

 puscles, there seems to be little doubt that they are derived in 

 the first place from the colorless cells (No. 2) known as erythro- 

 blasts. There has been some difference in the description of 

 these cells as given by various observers ; but there is enough 

 agreement to justify one in believing that the same cell is 

 meant by all, and that the erythroblast is converted to the 

 nucleated red corpuscle by the development of haemoglobin 

 in the cell protoplasm. This point might be regarded as gen- 

 erally accepted. The real difference of opinion lies in the 

 theories as to the derivation of the erythroblast. While Lowit 

 (29), Denys (14), and others believe that it constitutes a dis- 

 tinct variety of cell found in the marrow and other blood- 



