388 



VIII. Photograph representing a small artery in the 

 mesentery of the frog. Negative No. 184, New Series. 

 From preparation No. 826T, Microscopic Section. Magni- 

 fied 500 diameters by Wales's J-th objective, illuminated by 

 Calcium light. The preparation was made by myself. The 

 artery shown measures l-280th of an inch in diameter. It 

 is marked by both transverse and longitudinal silver lines. 

 The former are exterior to the latter, as is readily demon- 

 strated in the preparation by the use of the fine adjustment. 

 The longitudinal lines belong to the epithelium, while the 

 transverse markings indicate the boudaries of the circular 

 fibre- cells of the muscular coat' which are usually mapped 

 out in this manner in arteries of moderate size, the silver 

 solution reaching them by imbibition. The epithelial cells 

 of arteries of this size are narrower in proportion to their 

 lenuth than those of smaller twists, such as that shown in the 

 last two photographs. In the photograph it is somewhat 

 difficult, in many places, to make out their boundaries, as the 

 margin of the cells of the opposite wall come into focus and 

 complicate the appearance. In the study of the original pre- 

 paration this difficulty is readily overcome by manipulating 

 the fine adjustment. On each side of the artery, the numerous 

 nuclei of the surrounding tissue come more or less distinctly 

 into view. 



I X. Photograph representing the epithelium of a capillary, 

 in the muscular coat of the urinary bladder of the frog. 

 Negative No. 216, New Series. Fi-om preparation No. 3378, 

 Microscopical Section. Magnified 1000 diameters by Powell 

 and Leland's immersion l-16th objective, illuminated by the 

 Calcium light. The capillary which crosses the centre of the 

 field measures 1-S300ths of an inch in diameter. The epi- 

 thelial cells are narrower in proportion to their length than 

 those of the veins. Their nuclei are quite similar to those of 

 the venous epithelium. 



The foregoing description of individual photographs will 

 serve to give a correct idea of the epithelium lining the small 

 arteries, veins, and capillaries, as shown in a considerable 

 number of preparations preserved in the Museum, and as 

 observed by me many times in tissues extemporaneously pre- 

 pared. Both Balogh and Feltz would seem to have been 

 singularly unfortunate in their silver stainings, for they 

 describe the appearances produced as irregular and contra- 

 dictory. Balogh explains the black lines he occasionally saw 

 in the vessels after silver injections as due to the precijiitate 

 of silver occurring preferably on folds in the lining membrane, 

 caused by the irregular shrinkage of the vessel produced by 



