THE PRODUCTS OF THE TISSUE CHANGE. 563 



as specific products of the action of certain species of 

 bacteria ; they are only formed in large quantities under 

 the influence of a few fungi, and they then go hand in 

 hand with the best development and growth of these 

 species. It is more seldom that we meet with other 

 alcohols containing more carbon, such as mannite, vis- 

 cose, &c. ; these appear almost entirely to be specific 

 fermentative products of a few species of fission fungi. 

 In like manner we have, as rare and limited products of 

 the tissue change of the bacteria, the granulose of the 

 fungi, which become blue on the addition of iodine, and 

 the sulphur of the species of beggiatoa. 



These various products of tissue change are not, how- Variations in 

 ever, so limited to the species of fungi which produces oAfisne* 

 them that each species only produce one of the products ^^Tof * the 

 belonging to the same group ; on the contrary, we very alterations in 

 frequently observe that the same species of bacteria can 

 at the same time produce carbonic acid, fatty acids, 

 ferments, ptomaines, and colouring matters ; that they 

 can also excite fermentation, and eventually can, as the 

 result of their parasitic growth, set up disease in animals 

 or vegetables attacked by them. We have already, on 

 page 351, referred to this matter in the case of many 

 fission fungi. 



As regards the answer to the questions as to the 

 constancy and specific nature of the products of the 

 tissue change, it becomes clear from numerous observa- 

 tions that the individual species of bacteria cannot on 

 every nutrient soil furnish all the materials which it is 

 capable of producing, but that, on the contrary, many 

 products require the presence of special constituents in 

 the substratum, these constituents not, however, being 

 necessary for the life of the fungus. 



The variation in the shades of the pigment according 

 to the nutrient substratum points to some such influence 

 of external conditions ; and this influence is still more 

 marked, for example, in the case of the bacilli of 

 glanders and cholera, which only produce a brown 

 colouring matter on potatoes and not on any of the 

 other ordinary nutrient substrata ; and it is also shown 



