POWERS OF RESISTANCE OF BACILLUS 403 



older cultures; mannite and saccharose are not fermented 

 (Graham-Smith). 



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. 115, 116). 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-shaped masses 

 which stain deeply, and the protoplasm becomes broken up into 

 globules with unstained parts between (Fig. 117). Some 

 become thicker through- 

 out, and segmented so *] *' 

 as to appear like large ** 

 cocci, and others show / 

 globules at their ends, >^ 

 the rest of the rod 



appearing as a faintly .- '-r 



stained line. Occasion- ; / ^ 



ally branched forms are ' ' - *^V 



met with. The bacilli ,1 



are non-motile, and do -^ ^ / 



not form spores. ~^ 



Staining. They take 

 up the basic aniline 

 dyes, e.g. methylene- 

 blue in watery solution, v- 



with great readiness, FIG. 117. Involution forms of the diphtheria 

 arul taii dppnlv thp bacillus; from an agar culture of seven 



PV ' days' growth. See also Plate III., Fig. 13. 



granules often giving the Stained with carbol-thionin-blue. x 1000. 

 metachromatic reaction 



as described. They also retain the colour in Gram's method, 

 though they are more easily decolorised than the pyogenic cocci. 

 By Neisser's stain (p. 115) the granules are stained almost black, 

 the rest of the bacillary substance yellowish-brown, or by the 

 Dew method, pink (Plate III., Fig. 12). 



Powers of Resistance, etc. In cultures the bacilli possess 

 long duration of life ; at room temperature they may survive 

 for two months or longer. In the moist condition, whether in 

 cultures or in membrane, they have a low power of resistance, 

 being killed at 60 C. in a few minutes. On the other hand, in 

 the dry condition they have great powers of endurance. In 

 membrane which is perfectly dry, for example, they can resist a 

 temperature of 98 C. for an hour. Dried diphtheria membrane, 



