230 PRACTICAL BACTERIOLOGY. 



the Streptococcus pyogenes are formed^ but are never 

 so large, and are more transparent. Along the whole 

 track of the needle there are a large number of small 

 whitish spherical colonies, which do not coalesce. On 

 agar-agar a very delicate shining transparent coating 

 is formed, which also mainly consists of isolated colonies 

 which, however, are confluent in a few places. This 

 organism develops best in bouillon, which becomes 

 very slightly turbid. It is remarkable for the ex- 

 ceedingly slight power of resistance of its cultures. 

 They die off after a few days, and if their cultivation- 

 is to be continued, fresh inoculations must be made 

 every three or four days. 



It appears that this organism is not only the chief 

 cause of pneumonia, but also of various other diseases. 

 Moreover, it occurs very frequently in the mouth 

 cavities of perfectly healthy men. As a rule, therefore, 

 it appears to be a perfectly harmless inhabitant of the 

 mucous membranes of the mouth and nose, and only 

 under quite fixed, but at present unknown, conditions 

 does it acquire the power of setting up disease. Ap- 

 parently it is only able to spread when the resistant 

 power of the animal cells has become weakened, as, 

 for instance, after a chill, in consequence of which the 

 mucous membrane becomes inflamed, and pours out 

 fluid which affords a very favourable nutrient medium 

 for the bacteria. , ' 



Frankel's diplococcus is pathogenic in rabbits, in 



