DEPARTMENT OF EMBRYOLOGY. 83 



large amount of dye which was assembled in the infranuclear zone, instead 

 of forming a perinuclear rosette, as occurs in mesothelium. In well-stained 

 animals the dye granuales filled the entire portion of the cell between the 

 nucleus and the basement membrane. 



Having acquired in his previous study a familiarity with the reactions and 

 characteristics of the living cells of serous membranes, Dr. Cunningham has 

 been able to trace them after they become detached, and thus he has con- 

 tributed to our knowledge of the source of the cells found in serous exudates 

 under normal and pathological conditions. He finds characteristic, desqua- 

 mated serosal lining-cells in the serous exudates at all times during a chronic 

 irritation. They degenerate rapidly and do not become clasmatocytes. 

 The clasmatocytes are derived from just one source, that is, the pre-existing 

 clasmatocytes of the neighboring subserosal tissues. The omentum is a great 

 storehouse for these cells, but they are present in all peritoneal territories. 

 His experiments show that all the polymorphonuclear neutrophiles, part of 

 the eosinophiles, and part of the monocytes that appear in inflammatory 

 exudates are derived by emigration from the blood-stream, while part of the 

 monocytes and possibly some of the eosinophiles are derived from the seat 

 of the inflammatory process. 



The completed paper on the distribution of clasmatocytes in various organs, 

 prepared by Dr. C. S. Beck, has appeared during the year. An account of 

 his observations was given in the Year Book for 1919. The study of Professor 

 A. M. Reese on the structure and development of the integumental glands 

 of the crocodilia has also appeared in its completed form. 



VASCULAR SYSTEM AND CHROMAFFIN GLANDS. 

 Blood and Blood-Vessels. 



In the report of this Department for the year 1920 reference was made to 

 the work of Professor F. R. Sabin upon the origin of the vascular system, as 

 observed in the living chick blastoderm. During the past year these investi- 

 gations have been continued, and with further improvement in methods Dr. 

 Sabin has been able to study the living membranes in the natural state and 

 under the influence of vital dyes for the first 7 days of incubation. With the 

 new technique she has made important observations on the origin and differ- 

 entiation of blood-cells and has brought the study of the blood into the field of 

 experimental cytology where the anatomist and physiologist may meet on 

 common giound. In her previous study she found in the living chick that on 

 the second day all the primitive blood-cells become erythroblasts and that 

 their genealogy is angioblast directly to erythroblast, or angioblast, endo- 

 thelium, erythroblast. In carrying the study to older, vitally stained chicks, 

 she finds that the primitive red cell shows a characteristic granulation ; on the 

 second and third day it takes the form of vitally stainable specific granules 

 and rods which form a wreath around the nucleus and completely fill the cell. 

 As the cytoplasm increases, this granulation is thinned out and the basophilic, 

 finely granular cytoplasm becomes more and more evident. Some specific 

 granules, however, are found in all of the red cells up to the time of hatching, 

 although the basophilia of the cytoplasm disappears. These reactions give 

 us a specific criterion for distinguishing the primitive red cell from the other 

 types of blood-cells; furthermore, one can recognize how primitive a given cell 



