454 PROTOPHYTA 



oxygen, there ^s great variation among Bacteria. This variation extends 

 from those forms, called aerobiotic by Pasteur, which require a plentiful 

 supply of free oxygen for the purpose of vegetation (e.g. Bacillus sub- 

 tilis, Cohn), to others (anaerobiptic) in which vegetation is promoted by 

 its exclusion (e.g. Bacillus Amylobacter, Van Tiegh.). Intermediate 

 forms occur between such extremes ; and Nageli has shown that 

 aerobiotic forms continue to vegetate when the supply of free oxygen 

 ceases. 



Speaking in general terms, what has been said already of the mode 

 of life of Fungi in other respects, e.g. nutritive adaptation, holds 

 good of such Bacteria as contain no chlorophyll. They are saprophytes 

 exciting fermentations and producing combustions of the substratum, 

 and putrefactive processes ; or parasites, though very rarely on living 

 plants, it may very well be on account of the acid reaction. As para- 

 sites in living animals they obtain the greatest share of our interest, 

 since, as everyone knows, it is sought to connect them with a large 

 number of diverse diseases. Thai this attempt is made with the 

 greatest rashness in many cases, on utterly insufficient data, often on 

 the mere presence of some vaguely determined form in diseased tissues, 

 is a scandal of medical literature. On the other hand it has been 

 thoroughly proved in certain cases that their presence and action have 

 the character of exciting causes of disease, and it cannot be doubted 

 that painstaking research will bring to light numerous other instances of 

 equal weight. Slipshod research will only retard progress in this direc- 

 tion. It has already done much in obscuring results, and in placing 

 obstacles in the path. The most noteworthy ijeature, as de Bary has 

 pointed out, in the parasitism of Bacteria in the living bodies of 

 animals is their facultative parasitism (as illustrated for example in 

 the well-established case of Bacillus Anthracis in anthrax or splenic 

 fever), a matter of grave importance from the medical point of view. 



Among saprophytes may be mentioned Bacterium Termo (Duj.), 

 an exceedingly abundant agent of putrefaction ; Bacillus Megaterium 

 (de By.) (fig. 380), and Beggiatoa alba (Trey.) (figs. 381, 382), the 

 ' sewage-fungus ' of engineers, found in sulphuretted waters, the effluents 

 from manufactories and sewage-works, which has a remarkable power of 

 extracting sulphur fr^n the water, and storing it up in the form of minute 

 refringent globule^. 



*As regards the position ofcBacteria, ' to say that they are offshoots of 

 the Fungi is to " contradict all trustworthy observations " so flatly, that 

 tri0 view need not be seriously discussed in this place' (de Bary, 'Comp. 

 Morph.,' &c., p. 474). ^They are only fungi in the very limited sense of 

 their b^ing 'thallophytes which contain no chlorophyll,' and indeed it 



