BY LI VI NG CUL TV RES. 43 1 



along with it a quantity of a culture of another organism 

 either in the living or dead condition. A few examples may 

 be mentioned. An attenuated diphtheria culture may have 

 its virulence raised by being injected into an animal along 

 with the streptococcus pyogenes ; an attenuated culture of 

 the bacillus of malignant oedema by being injected with the 

 bacillus prodigiosus ; an attenuated streptococcus by being 

 injected with the bacillus coli, etc. A culture of the 

 typhoid bacillus may be increased in virulence, as already 

 stated, by being injected along with a dead culture of the 

 bacillus coli. In such cases the accompanying injection 

 enables the attenuated organism to gain a foothold in the 

 tissues, and it may be stated as a general rule that the 

 virulence of an organism for a particular animal is raised by 

 its growing in the tissues of that animal. 



Combination of Methods. The above methods may be 

 combined in various ways. By repeated injections of 

 cultures at first attenuated and afterwards more virulent, 

 and by increasing the doses, a high degree of immunity 

 may be arrived at. 



Anti- Cholera Inoculation. Haffkine's method for in- 

 oculation against cholera exemplifies the above principles. 

 It depends upon (a) attenuation of the virus, that is, the 

 cholera organism, and (b) exaltation of the virus. The 

 virulence of the organism is diminished by passing a 

 current of sterile air over the surface of the cultures, 

 or by various other methods. The virulence is exalted by 

 the method of passage, that is, by growing the organism in 

 the peritoneum in a series of guinea-pigs. By the latter 

 method, its virulence after a time is increased twenty-fold, 

 that is, the fatal dose has been reduced to a twentieth of 

 the original. Cultures treated in this way constitute the 

 virus exalte. Subcutaneous injection of the virus exalte 

 produces a local necrosis, and may be followed by the 

 death of the animal, but if the animal be treated first with 

 the attenuated virus, the subsequent injection of the virus 

 exalte produces only a local oedema. After inoculation 

 first by attenuated and afterwards by exalted virus, the 



