CULTIVATION OF BACILLI. 



337 



I On gelatine at 22 C. a puncture culture shows a line of 

 | dots along the needle track, whilst at the surface a small 

 I disc forms, rather thicker in the middle. In none of the 

 j media does any liquefaction occur. In bouillon the organism 

 I produces a turbidity which soon settles to the bottom and 

 [ forms a powdery layer on the wall of the vessel, the upper 

 I part of the fluid being left clear. The medium becomes 

 I acid during the first two or three days, and several days 

 [ later again acquires an alkaline reaction. 



In these media 

 f the bacilli show the 

 I same characters as 



in the membrane, 



but the irregularity 



in staining is more 



marked (Figs. 84, 

 1 85). They are at 



first fairly uniform in 



size and shape, but if 



a culture is examined 



from day to day it will 



be found that their 



appearance gradually 



becomes irregular. Fi( . 85 ._ Diphtheria bacilli of larger size 



Many become SWOl- than in previous figure, showing also irregular 

 len at their ends into staining of protoplasm. From a three days' 



'club-shaped masses as %^3t^ th weakcarix>l-lach s iii. 



which are stained 



deeply, and the protoplasm becomes broken up into globules 

 with unstained parts between (Fig. 86). 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. These 

 are to be regarded as involution forms, and they occur more 

 quickly and abundantly on the media less suitable for their 

 growth, e.g., more quickly on glycerine agar than on serum. 

 The bacilli are quite devoid of motility, and they do not 

 form spores. 





