88 CARNEGIE INSTITUTION OF WASHINGTON. 



phagocytic activity shown by the peritoneal mesothelium in response 

 to intraperitoneal injections of granular suspensions and laked blood. 

 The clinical importance of being able to use the peritoneal cavity as 

 a route for the administration of therapeutic agents has led Dr. Cun- 

 ningham to continue his studies on peritoneal mesothelium, with the 

 view of determining particularly the degree to which such injections 

 are injurious or harmless to the peritoneum. From experiments 

 carried out with solutions of dextrose, he finds that this particular 

 substance can be injected without injury to the mesothelium. The 

 changes which occur over the diaphragm, spleen, and omentum are 

 in the nature of a stimulated proliferation; the swollen cells either 

 return to normal or are replaced by other cells within a few days. 



The more conspicuous morphological changes by which the bran- 

 chial vascular arches are converted into the permanent vessels of the 

 adult are already known, but before the factors that bring them about 

 can be understood a knowledge of the detailed development becomes 

 necessary. Our large collection of embryos and the associated facilities 

 of the Department have made it possible to undertake a more careful 

 study of these vascular transformations. Dr. E. G. Congdon, of 

 Leland Stanford University, is at present engaged in preparing a series 

 of reconstructions of the aortic arches as they are found in the human 

 embryo. Dr. Heuser has studied the same structures in the embryo 

 pig and, by using injection and clearing methods, has been able to 

 make important observations. A preliminary account of these has 

 already been published and the complete description is now in course 

 of preparation. 



Using some of the improved methods of injecting blood-vessels, 

 Professor F. R. Sabin has made a histological study of the process of 

 repair in end-to-end intestinal anastomoses. In addition to making 

 observations on the healing of the mucosa and the changes in the 

 smooth muscle, she was able to follow the regeneration of the blood- 

 vessels, a process which has a direct bearing on the fundamental 

 problem of the origin and differentiation of angioblasts. Dr. Sabin 

 has found that the regeneration of vessels is limited to specific areas 

 and that the growth of new vessels is preceded by a change in the endo- 

 thelium of the old vessels in the nature of a return to the original 

 angioblastic type, with a great multiplication of endothelial nuclei. 

 From such transformed vessels solid masses of angioblasts grow out, 

 acquire a lumen through liquefaction of their cytoplasm, and, after 

 passing through a capillary stage, become arteries and veins. The 

 picture corresponds closely to the origin of blood-vessels, described by 

 Dr. Sabin in the living blastoderm of the chick. 



UROGENITAL SYSTEM. 



The development of the external genitalia in the human embryo has 

 been studied by Professor M. H. Spaulding, who succeeded in finding 



