COSYNEBACTEBIUM DIPETEEBIJU. 391 



ponderance (60, xii). The other forms represented in 

 Plate 60, v-ix, also occur in true diphtheria, the short 

 forms especially in very young cultures. 



Schiitz found the best formation of branches in different 

 cultures to occur sometimes upon albumin, sometimes on 

 glycerin-agar; also, in distinction to C. Frankel, he often 

 observed beautiful branching in bouillon (Berl. klin. 

 Wochenschr., 1898, 297). 



Motility. — Never present. We have never seen any 

 motion at all. 



Staining Properties. — Stains with all the anilin dyes, 

 especially in young cultures; also by Gram's method. 

 Gram's method, especially as modified by Czaplewski, is 

 to be recommended for the study of smear preparations 

 from diphtheria material; carbol gentian- violet and Gram's 

 solution of iodin are used. (See Technical Appendix.) 



Carbol-fuchsin and anilin gentian- violet solution stain 

 very intensely, without revealing the finer structure. 

 Staining with warm LofHer's methylene- blue solution and 

 differentiating in water reveals a very characteristic struc- 

 ture in the bacilli. They consist of alternating sections of 

 intensely and faintly stained substaiice surrounded by a 

 delicate envelope of faintly stained material. This is most 

 marked in older cultures on blood-serum. Very young 

 bacteria stain uniformly blue. 



Metachromatic Granules. — Max Neisser has pointed 

 out that the occurrence of metachromatic granules permits 

 the differentiation of the diphtheria bacillus from many 

 related forms. According to Neisser, cultures are employed 

 which are made upon Lofiler's serum and kept at 35° (not 

 warmer) for nine to twenty hours (in older cultures the 

 granules disappear in part). The dried preparation is 

 stained for one to three seconds (Auckenthaler found ten 

 to fifteen seconds to be often better) with acetic acid methyl- 

 ene-blue solution (Technical Appendix), washed in water 

 (tap-water should only be used if it does not contain much 

 free COj), and then counter- stained three to five seconds 

 with a weak solution of Bismarck brown (Technical 

 Appendix). There is then observed a blue granule at one 

 or often at both ends in a majority of the brown-stained 

 bacilli ; not infrequently there are more than two such 



