312 BOTAMT. 



water. They occur in solutions of organic matter in im- 

 mense numbers, and are said even to appear in solutions of 

 inorganic salts under proper conditions.* 



278.— Order Baoteriacese. This includes the organisms 

 known as Bacteria, and which are present in fermenting and 

 putrefying matter ; they also occur in the blood and the air- 

 passages of diseased animals, and if not the cause, they appear 

 to be common accompaniments of many kinds of disease. 

 Oohn,f who has recently studied them, defines Bacteria as 

 " chlorophyll-less cells of spherical, oblong, or cylindrical 

 form, sometimes twisted or bent, which multiply themselves 

 exclusively by transverse division, and occur either isolated 

 or in cell-families." They elongate to double their normal 

 length and then become constricted in the middle so as to 

 form two cells ; branching never occurs. In the unicellular 

 Bacteria the cells resulting from division separate at once, 

 while in the filamentous forms they remain in connection, 

 forming strings or threads. Unicellular Bacteria sometimes 

 form a jelly-like mass by the swelling up of their cell mem- 

 branes ; this is the Zuoglcsa stage of Cohn ; it does not occur 

 in the filamentous species. " Bacteria frequently form an 

 oily stratum near the surface of a liquid (attracted by oxy- 

 gen) ;" to this condition Pasteur erroneously applied the 

 name " mucor,'' in his reports upon his experiments on spon- 

 taneous generation. Sometimes they form a tougliish pelli- 

 cle on the surface of the liquid, in which the Bacteria are 

 closely packed ; this is the " Mycoderma" of Pasteur's re- 

 ports. Lastly, when they have exhausted the nutriment 

 from the liquid, they form a pulverulent precipitate, which 

 may be regarded as a resting state. 



"Most Bacteria present a motile and a motionless condi- 

 tion ; the former is connected with the presence of oxygen." 



* See Bastian'8 " Beginnings of Life," Vol. II., Appendix. 



f "Researches on Bacteria" (Untersuch. iiberBacterien)in"Beitrage 

 zur Biologie der Pflanzen," Brfslau, 1872. See a rfisume of this paper 

 in Quarterly Journil of MMroseopical Science, 1873, p. 156. See also 

 English accounts of further researches by Cohn, 1875, 1876; in the 

 journal just cited, 1876, p. 259, and 1877, p. 81. Consult "The Bao- 

 teria," by Dr. A. Magnin ; translated by Dr. Sternberg. Boston, 1880. 



