128 Lectures on Bacteria. [^ xii. 



shown in a former Lecture that the Bacillus can not only 

 germinate and vegetate luxuriantly outside the body of the 

 animal, but that it forms its spores, in great profusion if the 

 conditions are favourable, only outside the animal. The con- 

 ditions for this non-parasitic development are the same as the 

 general conditions given above for saprophytes. A supply of 

 oxygen is required for perfect development ; the optimum tem- 

 perature for the formation of spores is 20-25° C. A great variety 

 of organic bodies can serve as nutrient material, as experiments 

 show, not only such as are of animal origin, for instance, por- 

 tions of an animal that has died of anthrax, or the often bloody 

 evacuations of diseased animals, or the meat-extract-solution in 

 which the culture of the Bacillus was first accomplished (see 

 page 12), but also many different parts of plants if they are not too 

 acid, such as potatoes, turnips, seeds, &c. On the moist surface 

 of such objects the Bacillus grows and forms extensive mem- 

 branous coverings, which at the close of their vegetation produce 

 countless spores. 



Thus it is evident that the Bacillus of anthrax belongs to the 

 class of facultative parasites, as described on pages 1 09, 1 1 o. It is 

 above all a saprophyte, for it is not only able to prolong its exist- 

 ence in the saprophytic mode of life, but it requires it in order to 

 attain to the highest phase of its development, the formation of 

 spores. On the other hand it is capable of parasitism, since it 

 finds its way into the proper host, and there acts as the exciting 

 cause of disease in the manner which has just been described. 



The phenomena attending the appearance of anthrax are now 

 completely explained in all essential points from the mode of 

 life of the Bacillus, if we take its existence for granted in the 

 same sense as that of any other animal or vegetable species. 

 The fact that anthrax when spontaneous usually appears in the 

 intestinal form, shows according to the knowledge which we 

 have acquired of it, that it passes in the spore-form from the 

 saprophytic into the parasitic state, and that the route which it 

 takes must be the same as that which serves for the food taken 



