BACTERIA. 387 



another Bacterium (' mother of vinegar '), the access of oxygen in abundance is 

 necessary. 



Putrefaction in the narrower sense properly affects only the proteid substances 

 which are decomposed by colourless, yellow, red and blue Bacteria, INIoist bread, 

 meal, boiled white of t^g, etc. exposed to the air for some time show in the first 

 place colonies of Bacteria at certain spots, which become extended more and more, 

 and which, in the case of the pigment Bacteria especially, are very conspicuous. It 

 is only necessary to touch these spots with a needle point, and then to touch with 

 the needle an Qgg boiled hard and deprived of its shell, and lying in damp air, to observe 

 at the infected spot within a few days a colony of Bacteria extending itself with all the 

 effects of putrefaction. The profound decomposition which the proteid substances 

 undergo under the influence of the Bacteria is most easily recognised by the escape 

 of evil-smelling gases — ammonia, sulphuretted hydrogen, and ammonium sulphide. 

 Finally, the proteid substances are completely destroyed. 



It is now scarcely doubtful that common Yeast, as well as Bacteria, are only 

 special vegetative forms of Fungi which consist of hyphae, just as the IMucor-yeast 

 is only a peculiar vegetative form of 

 Mucor racemosiis. Zopf has lately sho\\'n, 

 especially with respect to Bacteria, that 

 they arise by segmentation from exceed- 

 ing fine filamentous Fungi {Beggiatoa, 

 Cladothrix), and that these forms of Fungi 

 again proceed from them. The bacteria- 

 form of these Fungi reproduces itself, 

 under conditions favourable to nutri- 

 tion, by continually repeated transverse 

 divisions. Similar vegetative forms also 

 occur indeed in many Algae, and even 

 in the protonema of Mosses. The re- ,^:'"-. =48.-schi2omycetes. r sarar,^. 2. Bacuriu,,,. 



tr ^ 3. Vtbrio. 4. Sfirillum (after Cohn). 



markable and conspicuous facts in the 



Yeast-fungi and Bacteria, however, lie chiefly in their power of decomposing such 

 exceedingly large masses of carbo-hydrates and proteid substances by means of fer- 

 mentation, while they themselves make use of only small quantities for their growth. 



In the Yeast-fungi and Bacteria we have thus found the ferment-action accom- 

 panying nutrition proper, increased to a maximum. That a similar thing takes place 

 in other Fungi also, however, though to a smaller extent, is shown by the behaviour 

 of the common forms of Mucor, the mycelium of which, penetrating into sound 

 apples and completely permeating their parenchyma, is by no means satisfied with 

 extracting the material necessary for its nutrition : on the contrary, the substance of 

 the apple is decomposed into a soft mass smelling of alcohol and ethereal oils. 

 Apart however from what has been stated with respect to the ferment-fungi, a closer 

 insight into the chemical changes efi"ected by Fungi on their substrata is so far 

 wanting. The best we possess in this connection are Robert Hartig's statements as 

 to the destruction of wood by tree-killing Fungi. Before I quote his statements on 

 this subject, however, it will be well to make a few preliminary remarks with regard 

 to these Fungi. 



c c 2 



