500 A MANUAL OF BACTERIOLOGY 



Examination for the T. pallidum 



1. Examination in fresh preparations. Scrapings from the deeper 

 layers of the chancre, etc., may be emulsified in physiological salt 

 solution and examined microscopically, particularly with dark- 

 ground illumination (p. 139). 



Another useful method is the Indian-ink method. A scraping is 

 obtained from the lesion as above, and the fluid thus obtained is 

 placed on a slide and an equal quantity of ink added. The ordinary 

 commercial Indian inks may be used, Giinther Wagner's being 

 particularly good (p. 81). The ink must be examined microscopi- 

 cally to prove the absence of spirillar forms, which sometimes occur 

 in it. The serum and the ink are then rapidly and thoroughly 

 mixed and smeared over the slide so that a pale brown colour 

 results. The material dries in a minute or slightly less, and may 

 be examined directly with the oil-immersion lens, or the wet pre- 

 paration may be covered with a cover-glass and examined. 



The preparations, which keep for a considerable time, show the 

 red blood-cells as large clear circular areas in a brownish -black 

 field, the bacteria and debris as white rods, dots, etc., and spiro- 

 chaetes, as clear white spirals (Plate XXII. a). 



It is particularly important in using this method that in so far 

 as possible serum alone be used, and that a minimal amount of 

 mucous material or fibrin be mixed with the ink. The presence of 

 mucus results in the taking up of a large amount of the colouring 

 matter of the ink, with the result that a smear of the requisite 

 colour and thickness cannot be made. If too much serum is used 

 the albuminous material appears to precipitate the colour from the 

 fluid and a finely granular appearance is seen microscopically, which 

 is practically worthless for diagnostic purposes. Again, if too 

 much ink is used, the surface of the smear is increased in size to 

 such an extent that the task of examining it thoroughly is greatly 

 lengthened. 



Coles * notes a useful point in the recognition of the treponema, 

 namely, that if the number of turns of the spiral of the syphilitic 

 spirochaete be counted, six or seven turns will be found in a length 

 equal to the diameter of a red blood-cell. The distance from the 

 top of one spiral to the next is from 1 to 1-2 p. As red blood-cells 

 measure about 7-5 p in diameter, on an average six or seven turns 

 will be equal to the diameter of a red blood-cell. The treponema 

 varies in length from 6 to 15 p., or even more, and consequently 

 1 Brit. Med. Journ., May 8, 1909. 



