282 Description of a Totally Reflecting Prism. 



ternal cylinder {h), which is effected by a corresponding turn- 

 ing of the projecting ring (A;), forming the neck of the 

 speculum, the open sections of both tubes are brought into 

 coaptation, as is shewn partially by the dark space in Fig. 4, 

 and thereupon a similar portion of the mucus surface imme- 

 diately applies itself to the exterior of the glass tube within 

 contained. Illumination being afforded through the exterior 

 prism (c), as before explained, the interior one {d) in the 

 same manner transmits the light to the surface opposed to its 

 reflecting side, and a picture of this surface, in all the truth of 

 outline and colouring, is, simultaneously, thrown back on the 

 reflecting face of the prism, and so offered to the inspection of 

 the observer. By making the interior prism to course along 

 the open section of the speculum, every portion of the surface 

 exposed may be minutely examined. If the glass tube become 

 dimmed by exhalations or secretions before the survey of a 

 section is completed, it is merely necessary to turn it slightly 

 and to present a clean portion of its surface. Pursuing the 

 same method, neighbouring portions of the lining of the bowel 

 are to be included in the open aspect of the instrument, and 

 examined in the same manner until the survey of the whole 

 cavity is made. Let it be supposed that the open mouth of a 

 bleeding vessel is the subject of search ; the longitudinal aper- 

 ture of the speculum, in that case, may be contracted to a 

 chink, and this may be made to traverse the circle of the pas- 

 sage until the direct issue of the blood obviously corresponds 

 with the opening. If the case be not urgent, after the removal 

 of the glass tube, styptics or a caustic pencil may be applied 

 to the spot, as in common cases ; and if the haemorrhage is pro- 

 fuse, deluging the tube and the prism, we may probably be left 

 in doubt as to the situation of the bleeding vessel to the ex- 

 tent of a quarter of an inch. But it is surely calculated to 

 increase the chance of safety to the patient, to be enabled to 

 conclude, that in one certain small arc of the surface the cause 

 of danger is situated ; for, this being determined, a small cau- 

 tery, corresponding to the opening of the speculum, which in- 

 cludes the open bloodvessel, could readily be made to traverse 

 the isolated portion of the surface, and so to seal the issue of 

 the blood. Or, vsuppose the case under examination to be one 



