vii.] Relation to the substratum. Saprophytes. 65 



This is especially the case with organisms whose mode of life 

 is of the kind described and therefore with all that do not 

 contain chlorophyll, Infusoria and Fungi as well as Bacteria. 

 Fungi, especially in the narrower use of the word, Sprouting 

 Fungi, moulds, &c. being comparatively easy to examine, have 

 supplied the best and most numerous conclusions with respect 

 to the phenomena in question, and we shall often have to make 

 use of them as examples in the following remarks. 



The interest attaching to the Bacteria which are devoid of 

 chlorophyll rests chiefly on their effects on their substratum, and 

 after the foregoing introduction we must proceed to consider 

 these organisms, and endeavour to give a clear idea of them 

 by calling attention to the most important known examples. 



Organisms not containing chlorophyll are separated into two 

 primary divisions, according as the organic substratum is a 

 living or a dead body. Those which have their habitat on or 

 in living fellow-creatures, and derive their sustenance from them 

 are termed parasites ; the others which live on dead bodies are 

 known as saprophytes. Different species are in fact differently 

 adapted to one or the other mode of vegetation; some are 

 known both as parasites and saprophytes, others only in one 

 or the other character. 



We shall subsequently have to go more deeply into these 

 distinctions and gradations, especially in the case of parasites. 

 This brief mention of them is sufficient for the present. 



The particular account of these forms will be simpler and 

 more intelligible if it begins with saprophytes. The organic 

 compounds present in bodies inhabited by saprophytes are split 

 up into simpler substances; in extreme cases total oxidation, 

 rotting, takes place with the decomposition of non-nitro- 

 genous carbon-compounds into the final products of carbon 

 dioxide and water ; in other cases we have partial oxidations, 

 not proceeding so far as the final products of combustion, 

 ' oxidation-fermentations,' as for example in acetous fermenta- 

 tion that is, the formation of acetic acid by the oxidation of 



F 



