170 TEXT-BOOK OF BACTERIOLOGY. 



erally produces spores. These are endogenous forms which, in the 

 shape of shining- oval bodies, almost fill the entire cell and display 

 an exceedingly high degree of resisting power against exterior in- 

 fluences of all kinds. The most tenacious vitality as yet known in 

 micro-organisms is met with in the class of potato bacilli. Globig 

 found that the spores of one species were able to survive an expo- 

 sure of more than five hours to a jet of steam at 100 C. The potato 

 bacilli, as already stated, occurring frequently in substances con- 

 taining albumin, and liable to putrefaction, we must be particularly 

 careful when sterilizing, or when employing such substances 1'or 

 bacteriological purposes. A neglect of this precaution may lead to 

 unpleasant results. Thus, for instance, the unfortunate and much- 

 talked-about cancer bacillus proved to be nothing but a harmless 

 species of potato bacillus, whose germs had not been exterminated 

 in the blood -serum used as food medium. 



The potato bacillus thrives at incubator temperature and be- 

 longs to the aerobia. 



The bacilli readily take anilin stains; only when they are on 

 the point of sporulating, some portions of the cells show themselves 

 less sensible to the dyes. The fully-formed spores may be stained 

 separately. 



On the gelatin plate we see, first, yellowish- white roundish 

 spots, slightly granulated and with somewhat irregular edges. 

 When further advanced they liquefy the gelatin quickly and 

 strongly. The colonies then appear as gray circular depressions. 

 The microscope shows them as disc-like plates, with contents re- 

 sembling a ball of string, and with a tender, bright, white, finely- 

 patterned edge. Later on these distinguishing marks disappear 

 and the entire colony lies then as an impenetrable solid mass, with 

 fibrous outlines, in the midst of the liquefied gelatin surrounding it. 



In the test-tube also the gelatin softens rather quickly, and 

 much more energetically in the upper part of the puncture than in 

 the lower. The liquefied gelatin remains turbid from the granu- 

 lated, crumbly masses of the culture. On the surface a thin scum 

 forms, which appears folded and has a dull gleam. 



On agar the potato bacillus produces a thick, wrinkled crust, 

 of a dull white color, which can be easily raised and removed from 

 the surface on which it grows. 



On potatoes the peculiar manner of growth is seen still more 

 plainly. Here the bacillus speedily covers a whole slice with a 

 film which at first appears white, then grayish, and lastly brown, 

 and which displays numberless elegant foldings and windings, and 

 often appears as if strewn over with white powder. If we endeavor 



