The growth in this was fairly rapid and the smell very slight at the end of a week. A piece of washed sheep grain worked in this culture at 37° C. for four hours was considerably reduced, the grain was not attacked, the action differing in this respect from a prolonged puering. This mixed culture was grown in various other nutrient media, gelatin, gelatin and mineral salts, broth made from sheep and calf fleshings, etc., with practically the same results. In no case did the bating action equal that of dung, and was insufficient for practical purposes.

A cursory bacteriological examination of dung will show that the number of species of bacteria it contains is very large, but on making a plate cultivation from a sufficiently dilute infusion of fresh dog dung, most of the colonies developing appear to belong to four or five species. The following is a list of all the organisms which, so far as my knowledge goes, have been isolated from different kinds of dung:—

List of Known Bacteria in Dung.

1.Bacillus fluorescens putridusThese organisms have been formerly described as Bacterium termo by various authors.
2.  "    "   liquefaciens
3.Proteus vulgaris.
4.  "   mirabilis.
5.Bacillus subtilis.J. T. Wood, J.S.C.I., 1890, 28.
6.Micrococcus fulvus.
7.Bacterium ureæ. (Cohn.)
8.Bacillus saprogenes, I., II., III. Vide Herfeld, J.S.C.I., May 1895.
9.Bacillus butyricus.
10.B. putrificus coli.
11.B. pyocyaneus.
12.B. janthinus.
13.B. coprogenes fœtidus.
14.B. pyogenes fœtidus.
15.B. prodigiosus.
16.B. zenkeri.
17.B. magnus.
18.B. spinosus.
19.B. liquefaciens.
20.B. coli.
21.B. duclauxii = B. ureæ.
22.Micrococcus ureæ.
23.   "    " liquefaciens.
24.Proteus sulphureus.
25.Bacterium sulphureum.
26.Bacillus amylobacter.
27.Clostridium butyricum.
28.B. acidi paralactici.
29.Bacillus I.Isolated from horse manure by S. A. Severin, Centr.-Bl. f. Bakt. ii. [1], 97.
30.  "   II.
31.  "   III.
32.Spirillum serpens.Isolated by Kutscher, Zeit. f. Hyg. xx. 45.
33.  "  tenue.
34.  "  undula.
35.  "  volutans.
36.Vibrio I.
37.  "  II.
38.  "  III.
39.Spirillum from pig dung. Smith. Centr.-Bl. f. Bakt. xvi. [1], 124.
40.Streptococcus liquefaciens coli. Gamgee. Phys. Chem. ii.
41.Bacillus mycoides.[120]

There are besides many unnamed species of bacteria in dung, among which are the two following isolated by me from puer—

(a) Plate Cultures.—Small yellowish colonies, slightly fluorescent, liquefy the gelatin slowly. Rods resembling B. subtilis when at rest, but moving with a rapid undulatory motion. Cultures in nutrient gelatin have a considerable reducing action on skin.

(b) Plate Cultures.—Bluish colonies liquefying gelatin rapidly, micro-bacteria in pairs. Not so marked an action on skin as (a). The organism resembles Proteus vulgaris, but swarming islets not observed.

Of the species mentioned above, a pure culture of B. subtilis in meat broth, maintained for one week at 35° C., had no reducing action on skin. B. fluorescens liquefaciens had a moderate reducing action.

The species developing on the plates vary according to the age of the dung. In horse manure, according to Severin,[121] bacilli predominate in the early stages. At the end of two to three weeks micro-bacteria, cocci and diplococci make their appearance, while the bacillar form becomes scarce. In three months cocci predominate, forming zoogloæ; strepto- and staphylo-cocci and spirilli were seldom found. Yeasts and sarcina were never observed. From observations extending over several years it is evident that a similar cycle occurs in dog dung. When quite fresh it contains comparatively few bacteria; then certain groups of species take possession, causing decompositions in the dung; these in their turn give place to other species, which decompose the products formed by the first, so that no one species produces or can produce the complex chemical and physiological changes which take place, or the bodies necessary for the bating of skin, as has been supposed by some observers.

None of the experiments, either with mixed or pure cultures of bacteria, had a perfect reducing action on skin, although the action was considerably greater than that of the chemical solutions. It was found, however, that by adding a small quantity of the amines above mentioned to the bacterial cultures, the reducing action became nearly as rapid and effective as with dung itself; and it was, therefore, clear that the principal bating effect was due to a combination of two things, viz. an active growth of bacteria in the presence of amine compounds.