64 MEDICAL BACTERIOLOGY 



coccus stains with all the usual anilin dyes, capsule remaining unstained. It is 

 Gram positive. There are various special methods of staining to tint both the 

 cocci and surrounding capsule. 



Growth. The growth of pneumococci on culture media differs but slightly 

 from streptococci; the range of temperature at w,hich growth occurs is more 

 restricted, from 25C. to 4iC.; on solid media the colonies are more moist and 

 transparent than streptococci and, as a rule, lack the elevated convex appear- 

 ance of streptococci; under magnification intertwining chains and the lace- 

 like edge of streptococci colonies are not observed. On blood-agar, colonies 

 are dry, blackish, and do not cause hemolysis. 



Litmus milk is more intensely acidified and more regularly coagulated by 

 pneumococci. Pneumococci ferment inulin and acidify bouillon to a greater 

 extent than streptococci. Otherwise the development on culture media is 

 practically indistinguishable from streptococci. 



Pneumococci do not form spores. 



Resistance. Surrounded by sputum or other viscid fluids pneumococci are 

 more resistant to germicides than when brought into direct contact with the 

 germicide; for this reason 20 to 50 per cent, alcohol is more destructive, because 

 more penetrating than stronger, less diffusible substances, and will kill pneumo- 

 cocci in sputum in less than an hour. Pneumococci in masses of sputum dry 

 out slowly and remain viable for several weeks; in droplets, especially if exposed 

 to sunlight, they die in from a few hours to several days. They withstand low 

 temperatures for a long time, freezing for weeks or months being required to 

 kill them. Pneumococci are quickly destroyed by chemical germicides, in 5 

 per cent, carbolic or o.i per cent, bichloride of mercury solutions they are killed 

 in several minutes. Ethylhydrocuperin, 1:500,000 solution inhibits growth, 

 and i : 200,000 kills pneumococci in vitro in 3 hours at 75C. Morgenroth 

 and H. F. Moore have shown that sterilization of animals infected with the 

 pneumococcus can be accomplished with this agent but the toxic dose is so close 

 to the sterilizing dose that the danger of employing it precludes its therapeutic 

 use. In a hot-air sterilizer pneumococci are killed in less than % hour at 

 i2oC. In a moist state a temperature of from 55C. to 6oC. kills in less than 

 % hour. 



Toxin. Pneumococci produce an intracellular toxin; there is an antitoxin 

 prepared that can neutralize it. 



Agglutinins. Can be produced experimentally but are not present in the 

 serum of infected individuals in sufficient quantity to permit agglutination tests 

 with the patient's serum for diagnosis. 



Antipneumococci sera for therapeutic use were more unsatisfactory prior 

 to the work of Cole than at present. 



Complement fixation tests are not employed in diagnosis. 



Bacterial vaccines do not confer immunity but are valuable adjuncts in the 

 treatment of certain cases. 



Pathogenesis. Pneumococci have their virulence increased by passage 

 through animals and lessened by cultivation or existence outside the animal 



