412 



NOTES. 



The Tubercle Bacillus. 

 By Edward M. Nelson. 



Twenty-four years have now passed since the publication by 

 Dr. E. Koch of his discovery of the tubercle bacillus. He 

 differentiated it from its surrounding material by staining it with 

 methylen-blue and vesuvin. He described the bacilli as being 

 very small rods, in length about \ the diameter of a red blood cor- 

 puscle, and in breadth about \ of their length.* In the same year 

 these rod-shaped organisms were resolved by me into beaded 

 structures.! At that time, owing to the imperfections of the 

 staining method, the beading on these bacilli was very difficult to 

 demonstrate ; but shortly after a new method of staining was 

 introduced by Dr. Ehrlich (Dr. Koch's assistant) which enabled 

 the organisms to be seen with a dry lens.J Ehrlich's method was 

 further improved by Dr. H. Gibbes,§ and so distinct were the 

 bacilli in his preparations that I was able to bead them with a 

 ^q objective. 



An average specimen of this organism as prepared by Dr. Koch 

 was in appearance like a row of rounded beads, eight in number, 

 but in a preparation by Dr. Gibbes there would only be four beads ; 

 they would, however, be larger and more widely separated ; so 

 that on the Koch's slide they would count 70 to 80, and on the 

 Gibbes' slide 35 to 40 in one-thousandth of an inch ; therefore beads 

 which were difficult to demonstrate on a Koch's were easy to see 

 on a Gibbes' slide. This may be explained by supposing that an 

 average specimen of the tubercle bacillus consists of four cells, 

 and that with Koch's method the stain only enters the ends of the 

 cells, leaving the centres unstained, while in Gibbes' preparations 

 only the central portion of the cell is stained. Fig. 79 shows a 

 bacillus stained by Koch, and fig. 80 one by Gibbes ; in fig. 79 

 the edges of the cells, and in fig. 80 the edges and divisions between 

 the cells, have been inserted to illustrate the above supposition. 



Further improvements in the technique of staining were made, 

 notably by Mr. J. C. Pound, F.E.M.S., who in 1889 prepared some 



* Vcrh. Physiol. Geaell. Berlin, 1882, p. 65; Lancet, 1882, pp. (>55-b\- J.R..VLS. 

 1882, pp. 385-8; Naturforscher, xv. 1882, pp. 149-50. 



t Kng. Mech., xxxv. (1882) p. 378(2 figs.). 



X Bull. Snc. Belg. Micro., vii. (1882) pp. cxvii.-cxxii. ; Berl. Klin. Wochenachrift, 

 May 6, 1882 : J.R.M.S., 1882, pp. 572-4. 



§ Luncet, 1882, ii. pp. 183-4; Brit. Med. Journ., No. 1137 (1882) pp. 735-6 ; 

 J.E M.S., 1882, pp. 895-7, aud 1883, pp 704-5 ; Lancet, 1883, i. p. 771. 



