Vital Resistance 497 



characteristic and enables the organism to be separated 

 without difficulty from the streptococcus. 



Gelatin Punctures. In gelatin puncture cultures, made 

 with 15 instead of the usual 10 per cent, of gelatin, the 

 growth takes place along the entire puncture in the form 

 of minute whitish granules distinctly separated from one 

 another. The growth in gelatin is always very meager. 



Agar-agar and Blood-serum. Upon agar-agar and blood- 

 serum the growth consists of minute, transparent, semi- 

 confluent, colorless, dewdrop-like colonies, which die before 

 attaining a size which permits of their being seen without 

 careful inspection. Upon glycerin agar-agar the growth is 

 more luxuriant. The addition of a very small percentage 

 of blood-serum greatly facilitates the growth. 



Bouillon. In bouillon the organisms grow well, slightly 

 clouding the medium. With the death of the organisms and 

 their sedimentation, the medium clears again after a few 

 days. 



Milk. Milk is an appropriate culture-medium, its casein 

 being coagulated. Alkaline litmus milk is slowly acidified. 



Potato. The pneumococcus does not grow upon potato.* 



Vital Resistance. The organism usually dies after a few 

 days of artificial cultivation, and so must be transplanted 

 every three or four days. In rabbit's blood, in sealed tubes 

 kept cold, it can sometimes be kept alive for several weeks. 

 Hiss and Zinnserf find that when the organism is planted in 

 " calcium-carbonate-infusion broth" and kept in the ice-chest, 

 the cultures often remain alive for several months. Bordoni- 

 UffreduzziJ found that when pneumococci were dried in 

 sputum attached to clothing, and were exposed freely to the 

 light and air, they retained their virulence for rabbits for 

 from nineteen to ninety-five days. Direct sunlight destroyed 

 their virulence in twelve hours. Guarniere found that dried 

 blood containing pneumococci remained virulent for months. 



The pneumococcus is destroyed in ten minutes by a tem- 

 perature of 52 C. It is highly sensitive to all disinfectants, 

 weak solutions quickly killing it. 



* Ortmann asserts that the pneumococcus can be grown on potato at 

 37 C., but this is not generally confirmed. The usual acid reaction of 

 the potato would indicate that it was a very unsuitable culture-medium. 



t Loc. cit. 



I "Arch. p. 1. Sc. Med.," 1891, xv. 



"Atti della R. Acad. Med. di Roma," 1888, iv. 

 32 



