Description of a Totalis/ Bejfecting Prism, 279 



experience may be brought to bear upon such diseased parts 

 with increased confidence and effect. Among the altered con- 

 ditions produced by disease which come under our observa- 

 tion in the living body, change of colour is at once the most 

 obvious, and in all its diversities the most significant, mark 

 which presents itself. From the first evanescent blush of 

 erysipelas to the inky stains of gangrene, and in the various 

 forms of eruptive disease there is scarcely need of farther in- 

 telligence than is gathered by the eye at a glance ; and when 

 the softer and more vascular textures within the mouth and 

 the other cavities of the body are the subject of morbid affec- 

 tion, the characteristics derived from the shades of colour, be 

 it of an inflamed, abraded, or ulcerated surface, are still the 

 most distinctive and important to be observed. The tutored 

 sense of touch, so far as that can extend, discerns somewhat, 

 nay much, of the conditions of disease even in the dark 

 cavities of the body ; but of colour, it cannot, at the present 

 day, form a better estimate than blind persons are said to 

 have done of scarlet when they likened it to the sound of a 

 trumpet. 



The advantage of Prismatic Illumination consists in the 

 opportunity it affords of examining the recesses of the open 

 cavities of the body by light of any desired intensity, and 

 that placed on either side of the observer, so as not to be 

 liable to be intercepted by his shadow, nor to interfere with 

 the freedom of any operative procedure ; and by the combina- 

 tion of two prisms, one placed at the external opening of the 

 speculum, the other moveable within it, so as to traverse its 

 extent, disease presenting itself at the opposite extremity of 

 the tube may be fully inspected, while through the transparent 

 sides of a glass tube, or the interrupted continuity of a metal- 

 lic one, the whole surface of the passage may in succession be 

 surveyed, and remedial appliances conducted to any point 

 affected with disease. Thus the numerous and serious affec- 

 tions of the straight-gut, whose nature is often obscure, and 

 the treatment uncertain and difficult, may derive all the ad- 

 vantages which light and the sense of sight are capable of 

 contributing in other cases. And these advantages are not 

 confined to the very limited extent to which touch can be 



