68 IOWA ACADEMY OF SCIENCES. 



but they were fortified and strengthened by Schwann, who demonstrated that fer- 

 mentation could not occur unless germs were present. The presence of these 

 organisms was not denied. Braconnet (1831), Berzelius (1827) and Liebig, that 

 briUiant, but conservative chemist, strongly held that these ferments simply 

 accompanied the process of fermentation. Some held that the action of these fer- 

 ments was entirely catalytic. Schwann, however, showed that various substances 

 heated sufficiently under ordinary conditions will decompose, but if the air before 

 having had access is heated, putrifaction did not occur. Schroeder and von Dusch 

 were able to show that these precautions are not necessary, since a cotton plug will 

 completely filter out all germs, and owing to this, which now seems a small mat- 

 ter, bacteriology has accomplished wonders in modern medicine and the arts. 

 Hoffmann, Chevreul and Pasteur demonstrated that cotton is not essential for 

 holding out germs. This can be done by simply drawing a tube out and bending 

 it. As the germs simply follow the law of gravity they cannot enter. 



In rapid succession the work of Pasteur, Klebs, Lister, Rindfleisch, Burden- 

 Sanderson set at rest the theories of spontaneous generation. They are no longer 

 advocated. All existing bacteria arise from pre-existing forms; so much is settled. 



Bacteria are, no doubt, subject to the same general laws as to the origin of 

 species as other living beings are; their growth and reproduction is determmed in 

 a measure by surrounding conditions. Bacteria are, no doubt, modified by cli- 

 mate and environment as are other living plants, but as yet we know little about 

 this. 



We may now ask, what are bacteria? Undoubtedly, plants amongthe lowest in 

 the ves'etable kingdom. In form, method of growth, and reproduction, they 

 strongly resemble Schizophi/cece. Chlorophyll is absent. A few of the species 

 described by Engelmann'' and Van Tiegham^ like Bacillus chlorinum and B. virens 

 have Chlorophyll, and hence apsimilate, but it may be doubted whether these forms 

 are bacteria. They are, no doubt, closely related, and are important links in the 

 chain of evidence showing the relation of bacteria to some of the algse. With 

 these exceptions they are fungi which do not form true hyphag. nor do they make 

 a true apical growth or branch; pseudobranching occurs in forms like Cladothrix. 

 In shape bacteria are round, elliptical, rod-like comma, and spiral, sometimes 

 growing in threads, and now and then certain aberrant forms. A peculiar group 

 is found in Dr. Thaxter's' Myxobacteriaceae, which resemble Myxomycetes. "These 

 consist of motile, rod-like organisms, multiplying by fission, secreting a gelatin- 

 ous base and forming pseudoplasmodium-like aggregations before passing into a 

 highly developed cyst-producing resting state, in which the rods may become 

 encysted in groups without modification or may be converted into spore masses." 

 Bacteria reproduce by division, the cell divides and two new individuals are formed. 

 Many species form spores; these are usually of the endogenous character; a few 

 form arthrospores, as in Leuconostoc and Cladothrix . In this genus we have the 

 curious anomoly that C. intricata, Russell, branches like Cladothrix and forms 

 eudospores like Bacillus^. 



The cells are all provided with a cell-wall which appears to be made up of cel- 

 lulose. Many of the species have motion, and this is in all cases probably due to 



5Bot. Zeltung, 1882, p.321. 



6 See Fluegge Mikroorganisms, p. 289; DeBary Bacteria, p. 4, 



7 On the Myxobacteriacere, a new order of Schizomycetes, Contributions from the 

 Cryptogamic Laboratory of Harvard Uaiversity, XVIII. Bot. Gazette, vol. XVII., pp. 

 389, 406, with plates XXII.-XXV. 



sZeitschrift fur Hygiene Vol. XI.,!1891, p. 192. 



