474 THIRD PART. BACTERIA OR SCHIZOMVCETES. 



exact investigations into the morphology and life-history of these plants. It results 

 from these investigations that the forms above described as cocci, rods, filaments, are 

 growth-forms, like a tree or shrub, a Filamentous Fungus, Sprouting Fungus or 

 Fungus-body. It has been shown by Cienkowski, Neelsgn, Hansen and Zopf, that 

 there are species which can assume the different growth-forms one after another, 

 sometimes with astonishing rapidity. R. Koch, Brefeld, Prazmowski, and Van 

 Tieghem, have made us acquainted with other species with greater uniformity of 

 growth, and Buchner has shown that external causes give rise to variations in the 

 same growth-form in one or more of these species. These investigations all confirm 

 the view advanced by Cohn, that there are species of Bacteria corresponding to the 

 species of higher organisms, but the distinctions between them are not those of 

 Cohn's form-species. There are comparatively uniform species, though they may be 

 capable of some variation, such as Bacillus subtilis, B. Anthracis and B. Megaterium ; 

 on the other hand there are pleomorphous species, especially among the arthrosporous 

 Bacteria, which may appear first in one and then in other quite different growth- 

 forms. It may be assumed in cases of variation and great differences of form, that 

 external causes operate to determine the form, and that the growth-form may be the 

 result of an adaptation to varying external agencies, as happens in cases like that of 

 Mucor (see page 154), though the operation of these external form-determining 

 causes has not yet been demonstrated in all cases. In connection with this point it 

 may be considered probable, that the vegetative process of the different growth-forms 

 of a species may cause different results of decomposition in the substratum, and that 

 the decomposing effects of the same form may vary with the substratum. It is with 

 due attention to these considerations that the determination of the species of the Bac- 

 teria must now proceed, we may almost say, begin ; it is obvious that this must rest 

 essentially on the morphology of the organisms, while at the same time the physiological 

 relationships must not be disregarded in the course of the investigation. 



SECTION CXXXIII. As regards the place of the Schizomycetes in the 

 natural system, it is apparent from the foregoing statements that the course of their 

 development does not point to any close affinity with the Fungi. To say that they 

 are offshoots of the Fungi is to ' contradict all trustworthy observations ' * so flatly, 

 that the view need not be seriously discussed in this place. They are termed Fungi 

 only in the sense of their being Thallophytes which contain no chlorophyll, and 

 with reference only to the vegetative process implied by the absence of chlorophyll, 

 while the course of their development and their classification are entirely disregarded. 

 The species of Bacillus and Spirillum therefore which have been mentioned above as 

 containing chlorophyll are at all events no Fungi. 



The forms included above under the name of Arthrosporous Schizomycetes 

 show an unmistakeably close affinity with the chlorophyllaceous and phycochromaceous 

 Algae, which form the group of Nostocaceae in the wider use of the term as including 

 the Nostocaceae and Chroococcaceae. This has been generally allowed since Cohn 

 drew attention to the point in 1853, and it has been recently and very fully worked 

 out by Zopf. According to our present knowledge the Arthrosporous Bacteria are 



1 See Cohn, Beitr. II, p. 188. 



