304 TEXT-BOOK OF BACTERIOLOGY. 



The capsule remains usually unstained and appears in prepara- 

 tions as a pale, glistening envelope in which the bacillus lies imbedded. 

 But we may render the membrane accessible to coloring substances. 

 For this purpose, Friedlander recommends treating cover-glasses 

 and sections for twenty-four hours with an acetic acid gentian- 

 violet solution (cone, alcoholic sol. gentian- violet, 50 parts; aqua 

 dest., 100; acid, acet., 10) and decoloring them afterward in O.lj^ 

 acetic acid; followed by alcohol, cedar oil, etc. Even this method 

 is not always successful. 



The pneumococci grow on the gelatin plate (even at a relatively 

 low temperature — 16° to 20° C.) quickly into extensive colonies. They 

 rapidly advance to the surface of the gelatin without liquefying it, 

 and develop into thick and white accumulations of a china lustre, 

 with a strong central elevation arched like a button, with smooth 

 edges. The microscope exhibits brownish- yellow, clearly-circUm- 

 scribed, usually irregular colonies of slightly-granular texture. 



Growth in the test-tube proceeds in the beginning uniformly 

 along the entire inoculation puncture. But soon there develops on 

 the surface an especially prominent mass glistening like snow, 

 somewhat arched, and imparting to the culture, in combination with 

 the portion extending downward into the gelatin, a certain simi- 

 larity to a thick-headed nail. In the course of further- develop- 

 ment, gas-bubbles in more or less great numbers frequently arise 

 in the gelatin surrounding the inoculation puncture. A slight 

 brown coloring of the medium regularly takes place in older cultures. 



The pneumonia bacteria thrive on agar-agar as a moist, thick, 

 whitish film. They produce on potatoes a yellowish-white, smeary, 

 and very thick film in which a formation of gas-bubbles is some- 

 times observed. 



Friedlander was able to effect successful transmission to animals 

 from these artificial cultures. Rabbits proved completely insus- 

 ceptible; Guinea-pigs' were also only slightly sensitive; but the 

 desired result was obtained in a large number (thirty-two) of mice, 

 all of which died. Friedlander injected a dilution of his pneumo- 

 cocci through the thorax into the lungs. Section showed the latter 

 to be altered by strong inflammation, reddened, sometimes hep- 

 atized and void of air; the tissue contained, besides, large quantities 

 of bacteria available for further cultures. 



The direct injection into the lungs permits conclusions as to the 

 greater or less infectious qualities of the micro-organisms used for 

 experiments only with very great reserve. Hence, we must look 

 for other proofs tending to convince us that we have in the pneu- 

 mococci an actual cause of pneumonia. 



