POWERS OF RESISTANCE. 363 



an alkaline reaction. If, however, the bouillon is glucose-free 

 (p. 80) the acid reaction does not occur. 



In these media the bacilli show the same characters as in 

 the membrane, but the irregularity in staining is more marked 

 {Figs. 122, 123). They are at first fairly uniform in size and 

 shape, but later involution forms are present. 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. 124). 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 in agar or blood-serum cultures, which take the shape of 

 a three-rayed star usually. Lately, Hill has demonstrated the 

 fact that even more complex branching forms are by no means 

 rare and can be observed to, occur in " hanging-block " prepara- 

 tions upon a warm stage within the course of a few hours. 

 The bacilli are non-motile, and do not form spores. 



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

 lene-blue in watery solution, with great readiness, and stain 

 deeply, the granules often giving the metachromatic reaction 

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

 though they are more easily decolorised than the pyogenic 

 cocci*. 



Neisser has recently introduced the following stain as an aid to the diagnosis 

 of the diphtheria bacillus. Two solutions are used as follows : (a) i grm. 

 methylene-blue (Griibler) is dissolved in 20 c.c. of g6 per cent alcohol, and 

 to the solution are added 950 c.c. of distilled water and 50 c.c. of glacial 

 acetic acid; (J>) 2 grras. Bismarck-brown (vesuvin) dissolved in a litre of 

 ■distilled water. Films are §tained in {a) for 1-3 seconds or a little longer, 

 washed in water, stained for 3-5 seconds in (i5), dried, and mounted. The 

 protoplasm of the diphtheria bacillus is stained a faint brown colour, the 

 granules a blue colour. Neisser considers that this reaction is characteristic 

 of the organism, provided that cultures on Lbffler's serum are used and exam- 

 ined after g-24 hours' incubation at 34-35° C, but more extended observations 

 show that this reaction has only a relative value. Satisfactory results are not 

 always obtained in the case of films prepared from membrane, etc., but there 

 is no doubt that here also the method is one of considerable value. 



Powers of Resistance, etc. — In cultures the bacilli possess 

 long duration of life ; at the room temperature they may surviv-e 

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



