Reasoning along these lines I was led to try some cultures of air bacteria in my special medium, and I found that a good source of such organisms likely to have a useful effect was a sweating stove as used for the depilation of skins. The hair roots are loosened by bacterial action; the wool, when it slips, brings away with it the epidermis. The root portions of the wool were cut off and digested in water at 35° C., the liquid strained off and used for making plate cultures in the usual way. In making the attenuations for the plate cultures, the fourth was found to be practically a pure culture of the organism I have called bacillus d, or the sweating bacillus. It forms large whitish colonies, spreading on the surface, with irregular contour. The bacilli are very small, mostly in pairs, but sometimes joining together in thread-like forms. (Fig. [21].)
Grown in the special medium it had little or no action on skin. At the same time I found that a culture made from the original liquid, i.e., a mixed culture of the sweating organisms, had an exceedingly powerful bating action; indeed, the skin was bated more rapidly than with dung.
All the experiments carried out so far tend to prove that mixed cultures of suitable bacteria possessed the required action, whereas pure cultures do not. A further examination of the infusion of wool roots showed that the bacteria contained in it, consisted practically of two species only. The first of these I have already described, the second one, bacillus e (Fig. [22]), forms small brownish-yellow boat-shaped colonies on gelatin plates, very similar to one of the dung bacteria. They consist of plump cells, two or three times the size of bacillus d, united in pairs and short chains and surrounded by a capsule; the cells appear to vary considerably in size. Cultivated in the same way as the others it has very little action on skin. It is evident from these facts that the growth of the bacteria is a symbiotic one; separately they exert little or no action, whereas used together the action is most remarkable.
The author wishes to express his indebtedness to Mr. J. Golding, F.I.C., of University College, Nottingham, who made the first pure cultures of these “wool” bacteria.
The Influence of Solid Matter in the Bate.
In making comparative tests of my artificial bates and dog dung, I usually took the latter from the paddles in which it was diluted ready for use, and maintained both solutions at exactly the same temperature. Parts of the same skin were then digested in each solution, and the results noted after 1 1/2 hours. In order to make them more strictly comparable I filtered the dung bate, so as to employ the matter actually in solution when the bate was made up. It was found that the filtered bate had far less action than when it was used in an unfiltered condition. That this is not wholly due to the passing into solution of some of the solid matter during the bating was shown by adding an inert solid, viz., kaolin, to the filtered bate, when the action was greatly hastened. On adding kaolin to the artificial bate and keeping the liquid agitated, the same result was obtained. It seems that the finely-divided solid matter acts as a carrier for the enzymes, perhaps by a kind of mass action, each particle offering a surface vastly greater than the molecules of dissolved solids. In the case of “puer,” the organic insoluble matter is gradually brought into solution by bacterial action as the bating proceeds, though I do not believe this occurs to any great extent.
The following quantities of soluble and insoluble matter were found in puer wheels in actual practice per 100 c.c.:—
| — | 1 | 2 | 3 | 4 |
| Total solids | 10·20 | 8·63 | 8·64 | 3·26 |
| Soluble | 6·00 | 4·57 | 6·19 | 2·14 |
| Insoluble | 4·20 | 4·06 | 2·45 | 1·12 |
1. Wheel in constant use for a week.
2. Wheel freshly made up.
3. The same wheel after one lot of skins.
4. From pigeon dung bate pit.