Description of a Totally Beflecting Prism. 281 



bulb or obtuse cone, projecting beyond the edge of the metallic 

 tube, as shewn in the plate, so as to facilitate the introduction 

 of the speculum, and defend the surface of the passage from 

 injury. If the disease to be examined is seated in the axis 

 of the instrument, such as stricture, the glass tube is to be 

 withdrawn when it has reached the seat of obstruction, be 

 that at the distance of 5, 7, or more inches, and a beam of 

 light transmitted through the prism (c), which is appended 

 to the neck of the instrument, is then to be conducted and 

 made to rest on the part affected, until it be fully and satis- 

 factorily examined, in the same manner as already detailed in 

 describing the auriscope. In passing, it is to be observed, 

 that, while the mechanical method of pressure and dilatation 

 is the most suitable for the treatment of simple stricture, it 

 is obvious that we must forego this plan when the disease is 

 situated beyond cognizance by the finger, the hazard of pene- 

 trating the coats of the bowel being a far more likely conse- 

 quence of the use of instruments in such circumstances than 

 the forcing of the more unyielding parts affected with disease. 

 By the introduction of light, and by obtaining a view of the 

 precise seat and remaining dimensions of the strictured part, 

 the bougie suited to enter this may be selected, and by the 

 first interference relief may be afi'orded, and progress made 

 in the track of cure. 



This much may suffice to exemplify the service afforded by 

 the single prism employed to illuminate a surface at the ex- 

 tremity of a straight tube. For the examination of disease 

 afi'ecting the sides of the cavity, a second prism (o?) is to be 

 used, mounted on the end of a slender metal rod (e/), of a 

 length somewhat greater than the tube, in order that it may 

 terminate externally in a small knob or handle, whereby it 

 may be conveniently moved throughout the extent of the in- 

 strument. To obtain the service designed in this arrange 

 ment, the speculum inclosing the close coniform glass tube, is 

 to be introduced as before. The metallic part of the instru- 

 ment represented in the plate consists of two light cylinders 

 {g and /i), one within one another, from each of which a longi- 

 tudinal section of half an inch, extending nearly the whole 

 length, has been removed. By a semi-revolution of the in- 



