416 DIPHTHERIA 



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. 119, 120). 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. 121). Some 

 become thicker throughout, 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 stained line. Occasionally 



branched forms are met 

 ~ with. The bacilli are 



v non-motile, and do not 



j~'X form spores. 



>K Staining. They take 



3 up the basic aniline 



^1^ ? f "V 



*"' % *v' *V dyes, e.g., methylene- 



ue * n wa * er y solution, 

 with great readiness, 

 A and stain deeply, the 

 i.W-r-C^' v^. * granules often giving 



-, f ~."~* | the metachromatic re- 



action as described. 

 They also retain the 

 colour in Gram's 



-^e method, though they 



FIG. 121. Involution forms of the diphtheria are more easily de- 

 bacillus : from an agar culture of seven > 1,1 ,1 

 days' growth. See also Plate III., Fig. 13. colorised than the pyo- 

 Stained with carbol-thionin-blue. x 1000. genie cocci. By Neisser's 



stain (p. 117) the 



granules are stained almost black, the rest of the bacillary sub- 

 stance yellowish-brown, or by the new 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 membranes, 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, 

 kept in the absence of light and at the room temperature, has 

 been proved to contain diphtheria bacilli still living and virulent 



