That Bacterium termo (Ehr.) is not a single definite species; various forms and stages of other organisms have been described under this name. The various species of Proteus go through a wide range of forms during their development in which cocci, short and long rods, thread forms, vibrios, spirilli, and spirochætæ occur. Under special nutritive conditions Proteus goes through a swarm stage, in which condition it is capable of moving over the surface and in the solid gelatin. The Proteus bacteria are facultatively anærobic, they all cause putrefaction; P. vulgaris and P. mirabilis are the commonest and most active of all putrefactive bacteria. They do not secrete an unorganised ferment, but decompose albuminous bodies by direct action. They also produce a powerful poison, of which small quantities injected into animals produce septicæmia.
Tito Carbone ([60]) found amongst the products of P. vulgaris, choline, ethylenediamine, gadinine, and trimethylamine. Macé ([61]), criticising Hauser’s work, considers the cocci form of Proteus to be spores. Bienstock ([62]) believes the rôle of the Proteus group somewhat doubtful. He discovered (1884) another widely distributed putrefactive organism, which he called Bacillus putrificus; it is a spore bearing, drumstick shaped bacillus found in fæces; it is anærobic and specially attacks fibrin. Now fibrin is extremely resistent to the action of most putrefactive bacteria, and it is very probable that specific organisms ferment the different albuminous compounds in the same way that the different carbohydrates are each decomposed by specific ferments. A certain number of species of bacteria are able to decompose both carbohydrates and proteids. Tissier and Martelly ([70]) call these mixed ferments, and divide them further into two groups (1), mixed proteolytic ferments, including B. perfringens, B. bifermentans sporogenes, Staphylococcus albus, Micrococcus flavus liquefaciens, Proteus vulgaris, this group decompose albumin by means of tryptic enzymes. (2) Mixed peptolytic ferments are only able to attack the albumin when it has undergone a preliminary decomposition. This group comprises B. coli, B. filiformis, Streptococcus pyogenes, Diplococcus griseus non liquefaciens.
The second class of bacteria are those which are without action on carbohydrates, and only attack proteids; these consist of the true proteolytic bacteria B. putrificus, and B. putidus gracilis, and the peptolytic bacteria, Diplococcus magnus anaerobius and Proteus zenkeri, which can only decompose peptones.
These authors state that B. putrificus is always present in putrefying albumin, but always accompanied by facultative ærobes which favour the growth and development of the special putrefactive bacteria.
In the putrefaction of meat the reaction is first acid owing to the action of the mixed ferments on the sugars present. In the next stage ammonia is formed by the tryptic enzymes secreted by the ærobic bacteria, and so the anærobic organisms are enabled to develop. We can thus understand how it is that putrefaction proceeds more rapidly the more mixed ferments there are present, although these were formerly supposed to hinder putrefaction from taking place.
When meat is exposed to air it is first attacked by the mixed ferments, Micrococcus flavus liquefaciens, Staphylococcus, Bacillus coli, Bacillus filiformis, Streptococcus and Diplococcus, and becomes acid; at the same time, the presence of decomposition products of albumin may be detected, proteoses, amidoacids, amines and ammonia; the latter quickly neutralise the acids, and in three to four days the meat is alkaline, and has a faint putrid smell. Bacillus perfringens and Bacillus bifermentans sporogenes now make their appearance; the latter of these organisms produces amines, amido-acids and ammonia. In this stage the simple anærobic ferments are able to begin their work, and real putrefaction sets in; as this proceeds, the mixed ferments gradually disappear, and finally the only organisms remaining are Bacillus putrificus, Bacillus putidus gracilis, and Diplococcus griseus non liquefaciens.
Another organism, which appears to play an important part in the decomposition of animal bodies, is described by Klein ([63]); he found that in bodies, which had been buried from three to six weeks, bacteria such as B. coli and B. proteus had almost disappeared, and an anærobic bacterium, which he calls B. cadaveris sporogenes, was very active. It is a motile bacillus 2–4 µ long, with flagellæ all over its surface. Spores are formed at the rounded ends, giving it a drumstick form. It coagulates milk, the clot gradually dissolving. It grows on all the usual nutritive media, but only under strictly anærobic conditions.
In a paper, entitled “Fermentation in the Leather Industry,”[92] I gave a short account of the progress of putrefaction as it takes place in the animal skin, and also described some of the organisms I had observed in putrefying skin. A small piece of skin was placed in water and allowed to stand at room temperature. During the first two days there was little change, but on the third day a number of swiftly moving darting monads made their appearance. Some of these were propelled by flagellæ, but a few had assumed amœboid forms. A slowly moving bacillus consisting of a long straight rod, apparently broken up into cells exactly like the Vibrio subtilis, illustrated in the “Micrographic Dictionary,” was observed, accompanied by some species of spirillum. Higher organisms present were a Paramœcium and a colourless transparent piece of protoplasm, shaped like a dumb-bell, with a slow rotating motion. On the fifth day the number of vibrios and spirilli had greatly increased, some with a swifter motion than others. There were also many large infusoria present; one of a peculiar double form, which appeared to be a development of the dumb-bell shaped piece of protoplasm seen on the third day. On the seventh day the most striking feature was the great increase in the number of vibrios; the field of the microscope was crowded; masses of the bacilli could be seen clustered round small particles of the disintegrating skin as if feeding upon it; there were more infusoria, many of them short, boat-shaped monads, with a trembling motion, refracting light strongly; these evidently accompany the putrefaction bacteria, and assist in the final disintegration. On the ninth day the piece of skin was entirely dissolved.
Procter calls attention to the relative putrescibility of the different constituents of skin, and especially to the rapid putrescence of the lymph and serum. So far as I know, this part of the subject has not been studied at all thoroughly, and there is a considerable field open to workers in our research laboratories.
Pure fat is not decomposed by bacteria, but if albuminous matter is present, the fat is split up by several species of bacteria and moulds. Schreiber ([73]) has shown that the presence of oxygen is necessary. As this subject scarcely comes within the category of putrefaction, I refer you to Schreiber’s paper, and also to an important paper by Otto Rahn ([74]) recently published.