70 IOWA ACADEMY OF SCIENCES. 



We may now briefly discuss the later classifications of bacteriologists. TheHe 

 begin with Davaine in 1868, who placed thein in the following genera. Bacterium, 

 Vibrio, Bacteridium and Spirillum. Hoffmann (1869) also adopted form as a leading 

 character. He lays stress upon the fact that motility is not a good character, that 

 this character may be absent or present depending somewhat on the conditions of the 

 medium and temperature. As he was not dealing with pure cultures hig observations 

 in this respect are of little value. Ferdinand Cohn", of Breslau, who devoted himself 

 largely to a study of bacteria smce 1853 formulated and adopted an excellent sys- 

 tem of classification which was largely followed, till better methods of culture 

 were in vogue. Cohn's work made a profound impression on the chaotic condi- 

 tion of the science at that time. Cohn was too able an investigator to rely 

 exclusively on the morophology of these organisms, for he states that germs cannot 

 be separated morphologically, since they will show different chemical and phy- 

 siological characters. He was not able to use many of these characters, since cul- 

 ture methods were very crude at that time. How far his predictions have held is 

 only too well known to workers in this field at the present time. He made three 

 groups — Chromogenic, Zymogenic fand Pathogenic, characters which certainly 

 find use in our present systems of classifications. Cohn believed that species of 

 bacteria could be established just as well in this group of plants as in more 

 highly developed organisms. The views of Cohn were not left unchallenged, 

 for in 1874 Billroth published his researches on Coccobacteria sepfica, an organism 

 which he obtained from milk serum. He argued that in different media the 

 same species varies greatly; he says " es gibt bis jetzt Keinerlei morophologische 

 Kennzeichen irgend einer Micrococcus-oder Bacterien form, aus welcher man 

 schliessen konnte, das-sie sich nur bei dieser oder bei jener Krankheit in oder am 

 lebenden Korper entwickeln konnte." Lister, who has achieved such renown 

 because of the introduction of antiseptic treatment of wounds, believed that mor- 

 phological characters used by systematists from Ehrenberg's to Cohn's time were 

 not to be relied upon, because he thought species changed in different media. 

 Thus he held that his Bacterimn lactis when grown in decoction of beets, urine 

 and other media presented quite different morphological characters. In some 

 media it had motion, in some it had not. He overlooked the fact that this 

 single drop of milk contained many organisms. The accomplished bacteriologist, 

 Buchner, at a much later day, thought Bncillus siihtilis, a harmless species, could 

 be converted under different conditions into Bacillus anthracis, a virulent patho- 

 genic germ. Dealing with such small objects and methods of culture in vogue at 

 that time caused a mixture of the two species. Is it to be wondered at that 

 mistakes should have been made and wrong conclusions drawn? 



We may conveniently now refer to the work of Hallier, a German botanist, who 

 became greatly impressed with the work of DeBary and Tulasne on the polymor- 

 phism of higher fungi. Why should not this polymorphism occur in 

 these small organisms? Luders had indeed advanced the theory that they 

 were connected with higher fungi. Hallier constructed a culture apparatus 

 in which his isolated germs were grown. Moulds of all kinds appeared, and the 

 same common moulds appeared m widely different cultures. He concluded that 

 the medium is the most important element in showing this polymorphism. He 

 states that it is nonsencical to describe separate species of yeasts and bacteria 

 with long names. His study of Asiatic cholera, diphtheria, glanders and other 

 contagious diseases convinced him that they had their origin in a Micrococcus 



uUntersuchung ueber Bacterien, Beitraege zur Biologie der Prflanzan, Vol. 

 1877, p. 127. 



