CULTIVATION OF THE BACILLUS 405 



(J. F. Smith), and, on the other hand, virulent organisms may not 

 conform. It is accordingly not possible to substitute fermentation 

 reactions for the virulence test. 



In culture media the bacilli show the same characters as in 

 the membrane, but the beading is a more marked feature, except 

 in the very youngest cultures, and sometimes the stained proto- 

 plasm has a sort of septate appearance (Figs. 114, 115). Some 

 varieties stain fairly uniformly with methylene-blue, but show 

 granules when stained by Xeisser's method. They are at first 

 fairly uniform in size and shape, but later involution forms may 

 appear, especially on the less favourable media, such as agar. 

 Many are swollen at 



their ends into club- ^^ r ^^7~~^^f>^ 



shaped masses which > ■ ' '• _ ■ >v ''^ x 



stain deeply, and the A * * ' / K 



protoplasm becomes « JSsi' ' x 



broken up into globules \ r , *' J 



with unstained parts be- . '■•&•£*', **vi / '-Y 



tween (Fig. 116). Some ,'. / \\ ^- ,j 1 



become thicker through- "* ft -< ■jf^Tk\>« 



out, and segmented so > - /A 



as to appear like large i'» s-C" - v~. jj '■ 



cocci, and others show — . - jf^ ^ 



globules at their ends, •- 



the rest of the rod ***| .. x '■•' 



appearing as a faintly ." 



stained line. Occasion- ** 



ally branched forms are FlG ' 116.— Involution forms of the diphtheria 

 ™~± —~ix* n^i. t_ 'ii' bacillus: from an agar culture of seven 



met with. The bacilli days . gn ; wth See al f Hate IIL| Fig . 13 . 



are non-motile, and do Stained with carbol-thionin-blue. x 1000. 

 not form spores. 



Staining.- — They take up the basic aniline dyes, e.g., 

 methylene-blue in watery solution, with great readiness, and 

 stain deeply, the granules often giving the metachromatic re- 

 action as described. They are Gram-positive, though they are 

 rather more easily decolorised than the pyogenic cocci. By 

 Xeisser's stain (p. 114) the bacilli are seen to contain granules 

 stained almost black, the rest of the bacillary substance being 

 yellowish T brown, or by the erythrosin method, pink (Plate III., 

 Fig. 12). In applying the stain a serum culture of 18-24 hours' 

 growth' ought to be used. The granules brought out by Neisser's 

 method are often not visible in a methylene-blue preparation. 



Neisser's stain is undoubtedly an important auxiliary in the recognition 

 of the diphtheria bacillus, but the results of its use are to be interpreted 



