It has been already mentioned that many of the microscopic fungi are ferments, aiding greatly in the decomposition of organic matter. They however are by no means the only agents in decomposition. The moment life is extinct in an animal or vegetable, Infusoria of the lowest grade seize upon the inanimate substance, speedily release its atoms from their organic bond, and restore them to the inorganic world whence they came. The ferment which transforms lactic acid into butyric acid is a species of vibrio which abounds in the liquid, isolated or united in chains; they glide, pirouette, undulate, and float in all directions, and multiply by spontaneous division. Vibrios possess the unprecedented property of living and propagating without an atom of free oxygen; they not only live without air, but air kills them. This singular property forms an essential difference between the Vibrios and the Mycoderms: the former cannot live in oxygen; the latter cannot live without it, and as soon as it is exhausted within the infusion, they go to the surface to borrow it from the atmosphere.
There are also two groups of Infusoria which possess these opposite characters, one being unable to live in oxygen, while the other cannot live without it; sometimes they even inhabit the same liquid. When the tartrate of lime is put into water along with some ammoniacal and alkaline phosphates, a Monad, the Bacteria terma, and other Infusoria appear after a time. These little animals bud rapidly in an infusion of animal matter, then a slight motion is produced by the appearance of the Monas corpusculum and the Bacterium terma, which glide in wavy lines in all directions in quest of the oxygen dissolved in the liquid, and as soon as it is exhausted they go to the surface in such numbers as to form a pellicle, where by aid of the oxygen they form the simple binary compounds water, ammonia, and carbonic acid. In the meantime the Vibrios, which are without oxygen, are developed below, and keep up the fermentation, and between the two, the work of decomposition is completed.
It is not the worm that destroys our dead bodies; it is the Infusoria, the least of living beings. The intestinal canal of the higher animals, and of man, is always filled during life not only with the germs of vibrios, but with adult and well-grown vibrios themselves. M. Leewenhoeck had already discovered them in man, a fact which has since been confirmed. They are inoffensive as long as life is an obstacle to their development, but after death their activity soon begins. Deprived of air and bathed in nourishing liquid, they decompose and destroy all the surrounding substances as they advance towards the surface. During this time, the little Infusoria, whose germs from the air had been lodged in the wrinkles and pores of the skin, are developed, and work their way from without inwards, till they meet the vibrios, and after having devoured them, they perish, or are eaten by maggots.