124 ON VARIABILITY AND ADAPTATION 



Hueppe and Cart-wright Wood. These observers gained from 

 ordinary earth a harmless saprophytic bacillus, in appearance 

 and mode of growth resembling closely the Bacillus anthracis. 

 Inoculated into mice, which are of all animals the most sus- 

 ceptible to anthrax, pure growths of the earth bacillus induced 

 immunity against this very fatal disease. 1 



On the observed Modifications of Pathogenic Microbes 



There is, however, another perhaps more satisfactory way 

 of approaching this subject of the occurrence of natural races. 

 I refer to the actual differences in mode of growth and properties 

 that are to be distinguished in cultures obtained from diverse 

 typical cases of any given disease. This subject has not been 

 worked out so fully as it deserves, nevertheless certain very 

 interesting observations have been made. Thus the Talamon- 

 Frankel diplococcus of acute croupous pneumonia has been 

 studied by Banti. 2 Banti describes four varieties of the species 

 Diplococcus lanceolatus capsulatus. No. 1 is the typical form de- 

 scribed by Prankel and Weichselbaum ; No. 2 is identical in form 

 and culture, but causes a " diplococcus septicaemia " in rabbits, 

 with small spleen and destruction of the red corpuscles ; No. 3 

 is similarly identical, but produces a septicaemia with moderate 

 enlargement of spleen and diffusion of haemoglobin ; and No. 4 

 only differs from the rest in that its virulence outside the body 

 disappears even more rapidly than is the case with the other 

 forms ; it produces a mild septicaemia associated with albumin- 

 uria, and the animals all recover. All were obtained originally' 

 from typical cases of pneumonia, and while in the years 1886, 

 1887, and 1890 the type form was alone gained from almost 

 every case of pneumonia — and these were of a benign nature — 



1 Hueppe and Wood, Lancet, December 7, 1889. [May it have been that 

 Hueppe and Wood's harmless saprophytic bacillus obtained from earth was the 

 B. mycoides of Thiele and Embleton referred to in Chapter III. of Part I. ?] 



* Banti, Lo Sperimentale, xliv., 1890, pp. 349, 461, 573. An observation 

 of Nikiforoff's may be quoted in this connexion (Zeitschr. f. Hygiene, viii., 

 1890, p. 531). Prom the lung of an influenza patient he obtained a microbe, 

 identical with the Diplococcus pneumoniae in every respect save that it pre- 

 served its virulence for longer periods and was fully virulent for mice, while 

 rabbits were completely refractory, whereas the true diplococcus is virulent for 

 both mice and rabbits. [It is interesting that renewed study of the pneumo- 

 ooccus has established the existence of four well-defined strains.] 



