Scientific Proceedings. 



123 



than from short (1-2 days) exposures. The length of exposure 

 required will depend somewhat upon the weather (strength of 

 light) and the thickness of the spread. ?>I ode rately heavy spreads 

 have given me better results than thinner ones, and impression 

 preparations better than smear preparations. In the shorter ex- 

 posures, some of the spirals will show uniform breaks between 

 the curves which may be attributed to the relation existing be- 

 tween spirochete and medium, the more superficial curves being 

 first impregnated. By longer exposure, the broken spirals are 

 made complete, probably by impregnation of the deeper-lying 

 curves. Disagreeable precipitation is not present on the serum- 

 covered film, but occurs on the adjacent uncovered glass. The 

 direct demonstration of silvered spirochetes may be taken as a 

 concluding proof of the microorganismal nature of the spirals. 



Other spirochetal organisms, from the buccal cavity, etc., may 

 be silvered by this method, and bacteria may also be silvered. In a 

 few comparative tests which I made, the degree of impregnation was 

 greatest with the pallida. Whether this is to be accounted for 

 by elective affinity or difference of medium in which the organ- 

 isms were embedded I cannot say. In the course of these exami- 

 nations, I came across examples of flagellated bacteria from the 

 buccal cavity in which the flagella were distinctly silvered. I 

 attempted to stain the flagella of certain bacteria — B. typhosus, 

 paratyphosus, pyocyaneus, hog cholera — from pure cultures, but 

 unsuccessfully. The terminal cilia of the pallida appeared not to 

 be stained by the silver. 



I have observed instances in which the silvered films showed 

 many more spirochetae pallida than the corresponding prepara- 

 tions stained by Giemsa's or Proca's methods. I shall mention 

 one instance in which in preparations from a macerated syphilitic 

 fetus, the number of pallida brought out by the silver impreg- 

 nation was very large, while very few spirals were found in the 

 Proca stained films from the adrenal gland and skin. The silvered 

 film from the skin showed small groups of pallida and a colony- 

 like mass such as I had not observed before in any film prepara- 

 tion. 



