10 



rial produced by the organism the whole mass being 

 termed zoogloea. Some are colorless, others pigmented. 



Of the bacilli, Cohn makes two genera bacillus and 

 vibrio ; others add more varieties. The members of 

 the genus bacillus are cylindrical rods ; they multiply 

 by fission, and some certainly exhibit a second mode 

 of reproduction the formation within their sheath of 

 minute globular or ovoid bodies, spores, which subse- 

 quently escape by rupture of the sheath (Fig. 4), and are 

 capable, under proper conditions, of growing again into 

 the rod form. These spores exhibit a tenacity of life not 

 possessed by the, mature bacilli, nor indeed by other 

 varieties of bacteria, since their vital activity is sometimes 

 unimpaired by prolonged boiling, or by immersion for 

 months in absolute alcohol, either of which procedures 

 destroys mature forms. The spores seem under ordi- 

 nary conditions the impersonations of immortality ; time 

 seems powerless to weaken them. 



In order to study the phenomena accompanying the 

 presence of bacteria in animal tissues, one must naturally 

 first identify the bacteria. Now this is a more serious 

 undertaking than the current literature on the subject 

 in our language would imply. A bacterium is a mass of 

 matter which possesses a definite size and shape, may or 

 may not exhibit motion, has a certain chemical composi- 

 tion, and is capable of growth and reproduction is, in 

 short, a living organism ; and no mass of matter can be 

 justly called a bacterium until proven to possess these 

 several characteristics ; for one or more of these several 

 properties may be exhibited by bodies found in the ani- 

 mal tissues which are not bacteria. 



An unfortunately large number of publications on this 

 subject exhibit by negative inference or positive demon- 

 stration, a failure to appreciate this self-evident fact. 

 Size, shape, and, above all, movement, are considered 

 conclusive evidence of bacterial nature. Size, shape, 

 and presence or absence of motion may be determined 

 by direct observation under the microscope ; distinctive 

 chemical traits may be detected by behavior toward cer- 



