306 TEXT-BOOK OF BACTERIOLOGY. 



pneumonia," especially after he had succeeded in finding it in the 

 hepatized pneumonia tissue of the diseased lungs and obtaining 

 pure cultures therefrom. 



This micro-organism has, according to Fraenkel's description, 

 the appearance of an " oval diplococcus, the links of which possess 

 an unmistakable similarity to the form of a lancet." Under high 

 magnifying power and by examining preparations of the blood 

 or tissue-fluid, it is found that here, too, one diameter of the 

 cells exceeds the other. The forms are never as distinctly rod- 

 shaped as those of Friedlander's bacteria, but the development of 

 the single members is not as uniform and regular as is usually 

 observed in true micrococci. 



The bacterium must, consequently, not be regarded as a coccus, 

 but as a bacillus, though it is usually still called " pneumococcus " 

 or " diplococcus," owing to the fact that Fraenkel's bacillus is usually 

 found in pairs, the pointed ends of the rod remaining united by 

 an interstitial layer. Handsomely-coiled chains of five or six ele- 

 ments often develop, but longer combinations are rare. 



Fraenkel's bacillus differs, therefore, from Friedlander's, inas- 

 much as the cells of the former are, on the whole, shorter, and . 

 longer members are wholly wanting; but both develop a capsule in 

 the animal body and never outside of it. In both, one cell and some- 

 times several are enveloped by the same capsule, which appears as 

 a glassy, lustrous halo or border. Practically both bacteria resem- 

 ble one another greatly, and have certainly often been confounded. 



Fraenkel's bacillus has no voluntary motion; it is semi- anaerobic, 

 being able to thrive without oxygen. It is strikingly sensitive to 

 the influence of temperature. It cannot develop at room tempera- 

 ture below 24° C, its optimum being near 37° C; higher tempera- 

 tures, say above 42° C, on the other hand, completely impede its 

 growth. 



It is to be remarked, further, that, according to Fraenkel's in- 

 vestigations, this bacillus requires a weak but distinctly- alkaline 

 reaction of the culture medium. Even small quantities of acid ren- 

 der its growth impossible, and the degree of alkalescence of the 

 medium is so important that the culture always fails whenever the 

 requisite alkalescence (easily ascertainable) is increased or dimin- 

 ished. 



It easily absorbs the common anilin colors, while thecapsule re- 

 mains intact. It is also accessible to double staining and can be 

 beautifully prepared by Gram's method — a very remarkable and 

 practically important difference from Friedlander's bacillus. 



Artificial culture outside the body is difficult. Gelatin plates 



