TEXT-BOOK OF BACTEEIOLOGY. I'l'l 



to remove a portion of this moist layer with the platinum needle, 

 we find that it is held together by the agglutination of the inti- 

 mately-joined bacteria. Thus one can draw out threads a foot 

 long, which are only held together by the shining, swollen envel- 

 opes of the separate rods. 



It is remarkable that the surface of the potato itself, under the 

 influence of the bacterial mass growing upon it, often takes a, 

 slightly-red, sometimes a decided red, color, which extends deep 

 into the substance. 



Bacillus Subtilis. 



The hay bacillus (Bac. subtilis — Ehrenberg) is one of the most 

 widely distributed and frequently occurring of all bacteria. As its 

 cells appear in the form of very large and clearly-recognizable rods, 

 it of course early attracted attention and became a subject of 

 study. F. Cohn observed the formation of spores in it, and a whole 

 series of facts, which were afterward found applicable to the bac- 

 teria in genera], were first noticed in connection with this particu- 

 lar species. 



The spores of Bacillus subtilis are found in the air and in the 

 water; the upper layers of the soil, the dust of dwelling-rooms, the 

 fseces of men and animals, putrescent fluids, etc., all contain them 

 in rich quantities. It has been called " haj' bacillus," from its being 

 regularlj' found in hay and in vegetable infusions of all kinds. If 

 we cut some dry grass into small portions, put them into a flask, 

 add a moderate quantity' of distilled water, close the vessel with a 

 pledget of cotton-wool, and boil for about a quarter of an hour, the 

 greater part of the germs contained in it are destroyed. Only 

 those of Bacillus subtilis, in consequence of their high power of re- 

 sistance, remain alive and capable of development, and after two 

 or three days a whitish covering forms on the surface of the fluid. 

 This covering or film consists of a luxuriant growth of hay bacilli. 



If we examine a small portion of it under the microscope, we see 

 large rod-like cells, somewhat slender, about three times as long 

 as they are broad, with slightly-rounded corners and perfectly 

 homogeneous, bright, translucent contents. The haj' bacillus has 

 a strong proclivity to form groups. Isolated cells are seldom ob- 

 served, and long threads crossing the whole field of the microscope 

 are by no means rare. This is the immediate consequence of its 

 energetic manner of growth. Attentive observers assert that a 

 cell can, under favorable circumstances, divide and become two new 

 ones by transverse segmentation within half an hour, and that this 



