Bacillus Subtilis, Hay bacillus, is a very common form, and, as its cells are large as compared with those of most bacilli, it is readily seen, and was early discovered. From its name, hay bacillus, it will be inferred that it readily occurs in vegetable infusions, being planted by the air. It is composed of rods, which are usually united into long threads. The bacilli are motile, possessing a flagellum at each end. Spore-formation occurs inside the rods, and as the spores enlarge the bacilli disintegrate so that the former are set free. If the spores are placed in a fitting medium they develop into rods. The membrane of the spore tears at one side and the young rod grows out of the cleft. This form grows readily on many nutrient media, forming on potatoes a whitish cream-like layer, and on other media a thick membranous layer. The hay bacillus is aerobic; deprivation of oxygen stops its growth. The hay bacillus has a superficial resemblance to the anthrax bacillus.