I IO 



Scientific Proceedings (38). 



question very naturally presents itself whether spontaneous lesions 

 could not be found more frequently if every vessel which appears 

 normal were examined microscopically. It seems plausible 

 a priori to suppose that before a lesion develops to such a degree 

 that it may be noticed on gross inspection, the beginning of it 

 may be so minute as to be discovered only by microscopical 

 examination. 



With this aim in view, 240 rabbits were examined. All these 

 animals were used for laboratory purposes, mainly for obtaining 

 blood-serum, and no toxic substance of any kind was introduced 

 into these animals. On gross inspection of the aorta of these 240 

 rabbits, 31, or 13 per cent., had gross lesions and these were not 

 examined any further. Of the remaining 209 animals, every arch 

 of the aorta (the part of the aorta which is most frequently affected 

 with spontaneous and arterial lesions) was examined microscopic- 

 ally. The specimens were hardened in formalin, imbedded in cel- 

 loidin or paraffin, and stained with hematoxylin-eosin and Weigert's 

 elastic tissue stain. Of the 209 vessels examined, 78, or 37.3 per 

 cent., presented minute lesions visible under the microscope. The 

 lesions showed either the degeneration of the media including the 

 muscular and fibrous tissue coat with the elastic fibers preserved, 

 but thickened and tortuous, or the same degeneration of the media 

 with loss of muscular and elastic fibers and deposition of calcium. 

 In other vessels, again, the main condition was proliferation of the 

 endothelial cells of the intima. 



Thus in our investigation we found in 52 per cent, of the ex- 

 amined rabbits arterial lesions of different degrees or development. 

 This percentage corresponds very closely to the percentage of the 

 diseased vessels found after adrenalin or other treatment. 



While the results of this research cannot prove with absolute 

 certainty that in some cases arterial lesions may not be produced 

 solely by the injections, the possibility seems to be great that the 

 treatment frequently only enhances or ripens an early stage of 

 arterial disease that existed in the vessel before treatment. It 

 would seem, therefore, that the rabbit is not a suitable animal for 

 the study of experimental arterio-sclerosis. 



