TEXT-BOOK OF BACTERIOLOGY. 173 



tures as saucer-like gray, translucent depressions in the gelatin; 

 the larger ones also present a similar appearance. As the growth, 

 beginning with the one original germ, proceeds with perfect regu- 

 larity in all directions, the colonies always form an exact circle, and 

 look as if stamped into the gelatin with a round punch. They are 

 of a delicate grayish- white color, but in the middle at the deepest 

 point they show a white spot, consisting of the first beginnings of 

 the colony which have sunk to the bottom. The principal mass, 

 consisting of gray, crumbly flakes, fills the rest of the space up to 

 the sharp white edge which separates the solid from the liquefied 

 gelatin. Frequently, too, a curious radiated " star-fish-like " ar- 

 rangement of the mass is observable. 



A much more striking picture is seen under the microscope. 

 In the centre lies a small, grayish-yellow, dense mass. This is 

 surrounded by an irregular entanglement of very thin fibres, which, 

 \)y careful examination with the ordinary magnifying power em- 

 ployed for examining colonies (for example, Leitz 3, Eyepiece 2, or 

 Bausch & Lomb f ", Ocular A), is seen to consist of separate rods 

 whose spontaneous movement may be recognized and watched. 

 The colony is surrounded, as it were, by a " corona radiata." The 

 bacilli which occup} 7 the foremost rank at the extreme edge always 

 bore vertically into the still solid gelatin, and stand like an army 

 with lances stretched out on every side. 



Thus the colonies of hay bacillus have such a characteristic ap- 

 pearance that they may at once be recognized, and cannot be mis- 

 taken for those of any other species. 



The same may be said of the hay bacillus test-tuoe cultures. In 

 the gelatin the strong liquefaction of course strikes the attention. 

 It takes place equally throughout the entire puncture. Very soon 

 the chief mass of bacteria sinks down in whitish flakes, the portion 

 of liquefied gelatin above them, which was for a time cloudy and 

 turbid, becomes clear, but on the surface there forms a dense, dry, 

 and brittle pellicle, looking as if composed of separate scales held 

 together by rods which have become immobile and have coalesced 

 into a zoogloea. 



On oblique agar the hay bacillus spreads out as a wrinkled, 

 whitish covering, arranged in regular folds and easily lifted from 

 the food medium. In its appearance it has a strong resemblance 

 to joints of a tape-worm. Blood-serum is quickly liquefied, also 

 forming a pellicle with folds. On potatoes the hay bacillus thrives 

 excellently; forming a white, cream-like covering, which, especially 

 in older cultures, contains great numbers of spores and also yields 

 involution forms of the rods. 



