168 VICTOR E. EMMEL 



In other respects these cells appear normal. The cytoplasm takes 

 a homogeneous hemoglobin stain. The nuclei are relatively 

 small and compact, and present a characteristic dark stain. In a 

 word, these erythroblasts present the appearance of having been 

 fixed at a stage in the process of constricting off a portion of the 

 hemoglobin-containing cytoplasm. The objection might be 

 raised that these forms instead of really representing stages in 

 the formation of plastids are merely the result of cells having 

 been fixed while compressed within the walls of narrow capillary 

 vessels, since as is well known erythrocytes are quite labile and 

 readily adapt themselves to passage through narrow spaces. 

 While some irregularities in the form of the fixed corpuscles may 

 be due to such factors, a number of considerations do not appear to 

 permit the disposal of the constriction forms just described in 

 this way. In the first place if these forms are due to compression 

 within capillaries it seems justifiable to expect their occurrence 

 in considerable numbers, especially in these membranes which 

 contain numerous capillary networks. On the contrary, however, 

 their frequency of occurrence is comparable to that of the telophase 

 of mitosis in the erythroblasts, so that it is necessary to search 

 rather carefully to find such constriction cells. Nor does this fre- 

 quency appear to vary under different conditions of fixation. For 

 example, since in some of these membranes fixation in situ took 

 place while the heart was beating, the precaution was taken to cut 

 the cord carefully just previous to fixation and thus eliminate a 

 possible congestion of the blood cells and consequent increased pres- 

 sure in capillaries as they were being penetrated by the fixing fluids. 

 However, no material difference was noted in either method of 

 of fixation. Second, compression in a uniform capillary tube 

 would seem to tend toward the production of a cylindrical elon- 

 gation of the cell rather than a constriction; while on the other 

 hand, mutual compression of a number of corpuscles packed to- 

 gether in a larger vessel tends towards the assumption of angular 

 or irregular rectangular forms, as may be observed in instances of 

 congestion. Third, the constricted forms may be found in both 

 large and small vessels, in association with erythroblasts under- 

 going various phases of mitosis, and under conditions where it 



