88 RETICULAR FIBRILS PRODUCED BY CAPILLARY ENDOTHELIUM. 



observed by Henle and Kupffer, for which Oppel had in 1890 discovered a method 

 of selective impregnation by a silver-chromate method, further proof of Mall's 

 conclusions as to the difference between reticulum and white connective tissue was 

 afforded by the application of Bielschowsky's silver-nitrate method to the staining 

 of these tissues. As shown by Ferguson (1912), successful impregnation of adult 

 tissues gives a totally distinct coloration of the two kinds of fibers. 



CORPUS LUTEUM. 



The present writer's interest in this subject began during his study of the origin 

 of the corpus luteum (Corner, 1919). It will be remembered that Sobotta, in his 

 well-known account of the formation of the corpus luteum of the mouse, states 

 that the connective-tissue framework is formed by the migration of the theca 

 interim cells inward among the granulosa and their simultaneous conversion into 

 "Spindelzellen." In the sow's ovary the author did not observe such a change of 

 the theca cells, but found that they remain interspersed among the granulosa lutein 

 cells of the fully formed corpus luteum, and like the latter are merely enveloped 

 by the interlacing fibrils of the connective tissue. Nor is there sufficient participa- 

 tion of the theca externa to provide fibroblasts to lay down the supporting frame- 

 work; indeed, in the fully developed corpus luteum one does not see, except perhaps 

 in the septa close about large vessels, any spindle-shaped cells which can be definitely 

 stated not to be components of capillary walls. As before mentioned, Clark, using 

 Mall's methods, has shown the connective tissue within the corpus luteum to 

 possess the characteristics of reticulum, and this observation is readily confirmed 

 by the Bielschowsky stain. In the presence of such a dilemma an organ plenti- 

 fully supplied with reticular connective tissue, yet without connective-tissue cells- 

 one could not fail to recall Mall's account of the condition in the liver. The endo- 

 thelium is the only possible source of the reticulum when we exclude the granulosa 

 and theca lutein cells. 



In order to test this hypothesis it was necessary to demonstrate the reticulum 

 by methods which do not at the same time destroy the other elements of the organ, 

 but which on the contrary give the sharpest possible pictures of the fibrils in their 

 relation to surrounding tissues. To this end the Bielschowsky-Maresch silver- 

 nitrate method proved best adapted. It was used exactly as directed by Ferguson 

 (1912), after fixation in 10 per cent formol, alcoholic formol, Bouin's fluid, or 

 Zenker's fluid. Sections were cut in paraffine at 4 microns. After impregnation 

 they were usually counterstained with alcoholic carmine. The Bielschowsky- 

 Maresch method has been extremely capricious in the author's hands, but when 

 successful the jet-black fibrils show against the red counterstain in the clearest 

 possible manner. Occasionally the cytoplasm is colored a deep golden brown by 

 the silver, and counterstaining is unnecessary. In order to display the capillary 

 net, vascular injections were made, but these for various reasons proved chemically 

 incompatible with the reagents used in impregnating the sections. Hence it was 

 necessary to rely upon the presence of erythrocytes in the capillaries, in cases where 

 the exact relations of the endothelium would otherwise have been dubious. This 



