228 PRACTICAL BACTERIOLOGY. 



less severe nature. It grows on tbe ordinary nutrient 

 media at blood teat as well as at ordinary room 

 temperatures. In plate cultivations it develops in 

 the form of white drops, which look like glistening 

 knobs of porcelain ; in stroke cultivations on agar- agar, 

 n slimy greyish- white layer develops ; in gelatine 

 puncture cultures a fairly thick white thread is formed, 

 whilst on the surface a similar knob is formed, which 

 looks like the head of a nail, so that this culture has 

 been called the nail culture. The bacilli are easily 

 stained with the usual watery aniline dyes ; they are 

 also easily decolourised, and, therefore cannot be 

 treated according to Gram's method. They are small, 

 short rodlets, generally occurring singly, but occasion- 

 ally joined together in pairs. In the human body 

 they are surrounded by delicate gelatinous sheaths, 

 which in preparations of sputum or in sections of 

 tissues do not become stained with the rest, but sur- 

 round the rodlets like bright, strongly refracting 

 zones. These sheaths or capsules are not seen in 

 bacilli derived from cultures. This Bacillus pneu- 

 monioe was considered by its discoverer, Friedlander, 

 to be a micrococcus, and was called by him the Pneu- 

 mococcus. 



An organism, discovered by Frankel, and now 

 called Diplococcus, occurs much more frequently in 

 croupous pneumonia. It is much smaller than the 

 Bacillus! pneumoniae, occurs generally in pairs, and is 



