Page:Science vol. 5.djvu/539

 Jure IB, 1885.]

��initrument needed is a round burette, tapering at both ends. &tid graduate *o tlmt the mark 100 1b exacLlj u the lower oriBce, and Ihe mark a few cenlimetrei below the upper (Bg. 7). On each ex. tremity li placed a rubber tube closed bj a apTing. Before using, I disinfect tbe apparatus by passing sulphurous acid through it, and then attaching It to ft Papln's pot filled with water at UO" C. for an hour. In Bfleeii minutes all Irnce of the sulphurous acid hae disappeared, both rubber tul)es are closed, their ends plugged with sterilized flax, and the burette left to cool. In cooling, a perfect vacuum is produced in the tube. I affix Lo the lower rubber tube a pointed canula, sterilized at llie time by a cur- rent of steam or the flame. introduce It Into a flask of lioulllon kept tor three or four weeks at 311° C. (lo prove its- complete scerill/atlon), open the lower spring, and ihe bu- Fio. 8.-BLiiii LIT- retle is filled immediately: Hi.' icna-rusK. fluid-is allowed to rest at the

The apparatus being Ilius prepared, a very dilute portion of the fluid, or a small piece of the substance containing the organisms to be separated, is Intni- duced at the (op of the hurelle. The dilution must be greal; for the contents of ilie burette can only h'-.

����distributed among twenty-Bve tuben, and more than two-lhirds of these lubes must become inoculated In r lo Ihe success of the experiment. H it be desired to determine the number of germs in a given ■peclmen of water, put a very minute quantity into

��the burette filled with sterilized houitlon; mix the two thoroughly, thus obtaining an equal dlstrlbuUon of the germs; Introduce the canula of the burette, immedlaiely after heating, through the plug of a Sterilized tube; allow four cubic centimetres of the fluid to flow from the burette; and so on tor tweuty- Qve tubes.

If all the lubes become cloudy, it is I>ecau9e the amountof waiernsed was loo great; and thlsamount must be reduced until only a portion of the tubes show any sign of life. With waier full of bacteria,

���the quantity lo l>e used is loo small for e: meat; and then two burettes are used, the one full of water, and the oilier of liouilion. A. drop of the suspected water is placed in the first, and then this dilution is used with the bouillon, aa before. A simple arithmetical calculation then gives the approximate number of germs in a given quantity of water.

The first esperlments of Pa.steur and Tyndall were imperfect in melliod; UIgiiet used a flock of cotton in a glass tube, through which be Bllered the air, and then washed the cotton in sterilized bouillon; my improvement is to substitute a powder, soluble in the nutrient fluid, for the cotton; and for this purpose I use common salt, well sterilized. This salt may bo turned into the burette, and the calculation made aa

The re'ulls obtained by fractional culture are al Ihe

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