72 IOWA ACADEMY OF SCIENCES. 



physiological observations. Dr. Sternberg-" has also recorded a very large num- 

 ber of observations on the bacteria found in connection with yellow fever. 



One of the most important works of its kind ever issued is Sternberg'fe^' Man- 

 ual of Bacteriology. This should be in the hands of every bacteriologist. The 

 descriptions are so thorough that little more need be desired. Most of the species 

 are easily identified by the diagnostic found at the end of the volume, while the 

 descriptions are very thorough and complete. 



CHARACTERS IN BACTERIA. 



It is convenient here to discuss what characters should be used in the descrip- 

 tion of bacteria. 



Those who have given any attention to the classification of Schizomi/cetes are 

 aware that the work of purely systematic botanists like Winter-, and Burrill's'^* 

 translation of the same; Trevi8an2\ DeToni, Cohn cannot be used or offer, in suf- 

 cient data, since morphological characters to separate species are not reliable. 

 Many species are of the same size and shape. The species, however, seem to be quite 

 constant in their morphological characters as shape and size do not appear to 

 vary much within a species. Cohn-^ largely used shape and color in the determi- 

 nation of species, l)ut this was largely pioneer work and many of the species defined 

 by him cannot be recognized, and this is worse as we go back in the history of this 

 science. Zopf -^ has been an earnest advocate of pleomorphism of species, and his 

 classification rests on this doctrine. But pleomorphism is not so general as was at 

 first supposed by Zopf. It is true that some species produce resting spores that 

 resemble cocci as in Anthrax and other bacilli, but they never vegetate as such. 

 But pleomorphism does exist in certain forms as in the group to which Cladothrix, 

 Beggiatoa, and Crenothrix belong. These are truly pleomorphic, at least if we are 

 to trust the work of those who have given the subject attention. In some forms, 

 culture experiments have shown that a certain amount of pleomorphism does exist 

 as in Cladothrix intrieata, Russell. But in many cases the facts of pleomorphism 

 have not been brought forth by culture experiments as was at first supposed. 

 FrsenkeP^ makes the statement that these organisms {Cladothrix, Beggiatoa) do 

 not belong to bacteria, although they may be closely allied, to them. " We may 

 therefore maintain that, thus far at least a many formed species of bacteria has not 

 been observed, and the rule one can distinguish by the growth and from clearly 

 recognizable genera and species of bacteria, which do not run into each other." 



Morphologically then, the different species are distinct, quite constant, although 

 many species are similar. Our main reliance must be on physiological characters. 

 And this is used nowhere else in the vegetable kingdom. Physiological charac- 

 ters are sometimes used in the classification of animals, as in the Hexacornllinna. 

 The Madroporice secrete stony skeletons while the Actinarice do not. In other 



20Report on Etiology and Prevention of Yellow Fever, U. S. Marine Hospital Serv- 

 ice. Washington, Government Printing office, ISaO. See p. 181. 



aiA Manual of Bacteriology, pp. 886. Illustrated by heliotype and chromo litho- 

 graphic plates and two hundred and sixty-eight engravings. New Yorli, Wm. Wood & 

 Co., 1892. 



22DlePllze. 



23The Bacteria, an account of their nature and effects, together with systematic 

 desoription of the species. Eleventh report Board of Trustees, Illinois State Uni- 

 versity, pp. 92-157. 



24 Genera e. Spec, delle BatteriaceEB, 1889. 



25Beitraege zur Biologic der Pflanzen, Vol. 11, p. 130. 



28 Die SpaltpUze, pp. 101 with 34 flsrures, Breslau, E. Trewendt. 188i. 



27 Text book of Bacteriology, English translation. 



