CULTIVATION OF PNEUMOCOCCUS. 191 



scrum growth appears as an almost transparent pellicle 

 along the track, with isolated colonies at the margin. 

 On agar media it is more manifest, but 

 otherwise has similar characters (Fig. 

 51). The appearances are similar to 

 those of a culture of streptococcus pyo- 

 genes, but the growth is less vigorous, and 

 is more delicate in appearance. A similar 

 statement also applies to cultures in gela- 

 tine, growth in a stab culture appearing as 

 a row of minute points which remain 

 of small size; there is, of course, no 

 liquefaction of the medium. On agar 

 plates colonies are almost invisible to the 

 naked eye, but under a low power of the 

 microscope appear to have a compact 

 finely granular centre and a pale trans- 

 parent periphery. In bouillon, growth 

 forms a slight turbidity, which settles to 

 the bottom of the vessel as a slight dust- 

 like deposit. On potatoes, as a rule, no 

 growth appears. Cultures on such media 

 may be maintained for one or two months, 

 if fresh sub-cultures are made every four 

 or five days, but they tend ultimately to FlG - 51- Stroke 

 die out. They also rapidly lose their pneumococcuT 611 ^n 

 virulence, so that four or five days after agar, showing a faint 

 isolation from an animal's body their streak with small semi- 

 , . . . , jj'--ij transparent colonies; 



pathogenic action is already diminished. two ys - ^^ at 



In none of the ordinary artificial media 37 c. Natural size, 

 does the pneumococcus develop a 

 capsule. (Guarnieri grew the pneumococci on the following 

 medium : meat infusion 950 c.c., NaCl 5 grm., peptone 25 

 grm., gelatine 40 grm., agar 3 per cent, water 50 c.c. This 

 medium at 37 C. is semi-solid, and in it Guarnieri states 

 the cocci developed capsules.) They usually appear as 

 diplococci, but in preparations made from the surface of agar 

 or from bouillon, shorter or longer chains may be observed 



