150 VICTOR E. EMMEL 



must be due primarily to the fact that the evidence was derived 

 from dried cover-glass preparations, for if one studies the fresh 

 blood either in the vessels of the membranes or on a slide under a 

 cover-glass sealed with vaseline where the plastids may be turned 

 over with proper manipulation it can be readily observed that 

 whereas some of these plastids are spherical, others are unquestion- 

 ably biconcave-disc or cup shaped. A few of the smaller elements 

 may be elongated and oval or even more or less rod shaped. 

 While the majority of the plastids have a smooth contour an oc- 

 casional one is found possessing a tapering cytoplasmic process 

 projecting from its surface (fig. 8; cf. pp. 138, 160, 170). 



2. THE ORIGIN OF NON-NUCLEATED RED CORP.USCLES IN BLOOD 



CULTURES 



Up to this stage of the present study attention has been directed 

 to cytological characteristics of the large nucleated red cells or 

 erythroblasts and the non-nucleated red plastids or erythrocytes. 

 This brings us to the long standing question as to the origin of 

 the non-nucleated elements,* whether they arise from the nucleus, 

 by an intracellular nuclear disintegration and dissolution, or by 

 some other process. Though many facts and much argument 

 have been advanced for various views, it does not appear that 

 the question can yet be regarded as settled. 



The usual methods of study employed in approaching the prob- 

 lem have consisted in the study of blood slides and sections of fixed 

 and stained vascular tissues. The diversity of opinion, however, 

 which still exists even after studies of this character, suggests 

 the desirability of other methods of attacking the problem. The 

 recently developed technique of tissue culture, with the striking 

 results obtained by Harrison ('07, '10), Burrows ('10, '11), Carrel 

 and Burrows ('11), Lambert and Hanes ('13), Lewis ('11, '12), 

 Loeb ('12), Oppel ('12) and others, lead one to expect that similar 

 methods may yield important data concerning the complicated 

 problem of the life history and genetic relationship of the various 

 types of blood cells — especially so when it is considered that 

 Jolly ('11) succeeded in keeping amphibian leucocytes alive 

 outside the organism for nearly a year. With this hope, a study 



