FISSION FUNGI AS CAUSES OF DISEASE. 637 



cell cannot be dissolved or penetrated by the majority of 

 bacteria ; some forms, it is true, can convert the dead 

 cellulose into sugar, or can cause it to ferment, but even 

 these organisms appear to be unable, under the other- 

 wise unfavourable conditions, to live in concurrence with 

 the living vegetable cells. On the other hand, in the 

 warm-blooded animals the bacteria find a substratum, 

 rich in albumen, faintly alkaline, and at a temperature 

 of about 37 C., and thus they have the most favourable 

 conditions for their development and multiplication; 

 hence the bacteria threaten the living animal with much 

 more serious dangers. 



Nevertheless, it is by no means all bacteria which are In animals, 

 able to live in the living animal ; on the contrary, we 

 can here also employ the classification given by de Bary, 

 of obligatory parasites, facultative parasites, and true 

 saprophytes. The species belonging to the group of the 

 saprophytes are much more numerous than the others; 

 bacteria, such as bacillus subtilis, micrococcus flavus, 

 bacillus erythrosporus, micrococcus aquatilis, and in- 

 numerable other forms, can be introduced in enormous 

 quantities into the veins, subcutaneously by the mouth, 

 or by inhalation into living warm-blooded animals 

 without causing any injury to the body. 



Among the facultative and obligatory parasites, the Various 

 different species show the most various degrees of patho- pathogenic 

 genie action. In considering this question it must be action - 

 remembered that the parasitic bacteria are often limited 

 to definite species or races of animals as their hosts, 

 and that not uncommonly the same species of bacterium 

 which in one class of animals excites a severe disease, 

 behaves in regard to another class as a pure saprophyte. 

 We shall enter more minutely into these important 

 differences in the chapter on " Predisposition " ; we need 

 only point out here that we are accustomed to reckon a 

 species of bacterium among the group of parasites if it 

 exerts pathogenic action on any one species of animal. 



The least amount of parasitic energy is shown by those Bacteria 

 bacteria which almost never multiply in the interior of ^^ ^ ns 

 the living body, but vegetate only on the surface, on the means of their 



