THE PUTREFACTIVE BACTERIA 227 



bacteria." In this general sense the term is used in Fig. 57. The figure itself 

 represents a species of bacterium (not more specifically identified) isolated from a 

 putrescent liquid. 



G. HAUSER (I.) investigated this matter more thoroughly, and showed, 

 especially, that Bacterium terino, in the sense implied by Cohn, does not exist. 

 In 1885 he brought to our knowledge three putrefactive fission fungi, which are, 

 moreover, bacteriologically important from their indisputable polymorphism, a 

 peculiarity since recognised in many other species of bacteria, but at that time 

 much disputed. Hauser's discovery was welcomed by the supporters of this 



B"IG. 57. Bacterium tcrmo. FIG. 58. Proteus vulgaris. 



Cilia staining-. Magn. about One long 1 rod and one short rod. Cilia staining. 



1500. (After photograms by Magn. about 1500. (After photograms by Fraenkel 



Fraenkel and Pfeiffer.) and Pfeiffer.) 



theory, and the importance attached to it at the time was expressed in the name 

 given to the organisms, Hauser having chosen the generic name Proteus for these 

 extremely mutable Schizomycetes. A short description of their characteristics is 

 subjoined. 



The cells of Proteus vulyarls are generally 0.9-1.2 p. in length, 0.4-0.6 Abroad, 

 and almost always occur in couples. In addition to these short rods, elongated 

 forms, very frequently attaining a length of 3.7 p., also occur. Some extremely 

 vigorous but very rare cells will measure 6 p. long by 0.9 p. broad. One of these 

 is shown Fig. 58. The large number of cilia indicates considerable locomotive 

 activity, and in fact this power is possessed by the various species of Proteus in 

 a high degree, manifesting itself both by a rapid forward movement and a con- 

 current (longitudinal) axial rotation. Hence, the coupled cells describe a kind 

 of double cone, the vertex of which is at their point of junction. In addition to 

 the above-named forms, gelatin cultures also yield spirilla, with two to four 

 convolutions; thread-cells, which may grow to a length of 100^1; and finally 

 " spirulina," or threads bent in the form of a bow, with ends twisted into a 

 queue. Under special circumstances involution forms are also produced : the 

 cells swell up in the shape of a pear, and resemble spermatozoa, dumb-bells, &c., 

 in form. 



Proteus mirabilis exhibits a very decided tendency for producing such involu- 

 tion forms. Globular or pear-shaped forms, 3-7 p, in diameter, are very frequently 

 developed in the cultures of this microbe, which also exhibits polymorphism in 

 a high degree, and in this particular greatly resembles the preceding species. 

 Here also we meet with short rods, long rods, spirilla, and thread-cells, rapidly 

 moving one through another in varied alternation. At the same time small 

 but unmistakable differences exist. Thus for example, these threads not unfre- 

 quently attain a length of 200 p., i.e. double the maximum size of the first-named 

 species. 



Proteus Zenkeri differs from the two preceding species mainly in its inability 

 to liquefy gelatin, but resembles them in other particulars, though its cells are 



