4O2 APPENDIX. 



duced under the basin with their cut surfaces, on which the inoculations 

 are to be made, uppermost. Various modifications of these methods may 

 be made by individual workers, but in most cases the potato used in the test 

 tube is the most convenient. 



Koch's Gelatinized Meat Peptone Medium. 



To prepare Koch's peptone meat jelly or solid gelatine medium, covei 

 one pound of beef, freed from fat and finely minced, with 1,000 cc. of water, 

 to which a drop or two of hydrochloric acid may be added ; allow the mix- 

 ture to stand in a cool place for twenty-four hours, and squeeze through a 

 cloth, as described in the preparation of meat extract. To this fluid add 10 

 grammes of albumen peptone, 5 grammes of common salt, and 100 grammes 

 (75, or even 50, if the weather be cool) of Coignet's gold label gelatine. 

 Mix in a two- or three-litre flask, boil for half an hour, or until the gelatine is 

 thoroughly dissolved, neutralize with the alkaline solution (p. 399), and again 

 boil for nearly an hour. Thisjength of boiling in some cases appears to be too 

 prolonged, the gelatine afterwards not becoming properly solidified. In such 

 cases it is necessary to add a little more gelatine, boil, and again neutralize. 

 The mass is then filtered through a layer of fine white filter-paper, moistened 

 with hot water in a funnel, which must be kept heated, to prevent solidifica- 

 tion of the gelatine on the filter. Salomonsen recommends a very ingenious 

 device, a device that may be used at almost any time, especially where only 

 small quantities of gelatine are to be filtered. He pours a little of the warm 

 gelatine into a filter which has been previously sterilized, warmed, and 

 moistened as follows : a layer of water is poured into a flask to the depth of 

 half an inch, in the mouth of which rests a funnel with a clean filter-paper. 

 The top of the funnel is covered with several thicknesses of filter-paper, 

 over which a sheet of asbestos or a plate of zinc is laid. By heating 

 the water to boiling-point for a few minutes, flask, funnel, and filter are 

 at once sterilized, warmed, and moistened. The hot water is then poured 

 from the flask, the funnel is replaced, its cover carefully removed, and the 

 gelatine is poured into it. If the flask be placed on a non-conducting sur- 

 face, a very considerable quantity of gelatine may be thus filtered. Where 

 larger quantities have to be filtered, it may be necessary to obtain a double 

 walled metal funnel, or, better still, an enamelled funnel with the limb 

 bent at an angle. This funnel is fitted into the top of the steam sterilizing 

 apparatus, the bent tube coming through the side. This, of course, can be 

 heated for any length of time, and is useful when large quantities of gela- 

 tine or agar-agar are dealt with. (This apparatus, which is comparatively 

 cheap, may be obtained from Frazer, Teviot Place, Edinburgh.) Before 

 filtering, it is sometimes necessary to clarify the gelatine by a process well 

 known to cooks. The gelatine is allowed to cool to about 50 C., the 

 white of an egg is broken into 100 grammes of water ; this, along with the 

 broken-up shell, is added to the gelatine, with which it is thoroughly mixed. 

 The whole is then boiled until the albumen coagulates and a perfectly clear 

 liquid appears between the flakes ; the mass is then filtered. 



Gelatinized Milk Serum. 



One litre of fresh milk is warmed to 60 or 70 C. Add from 70 

 to 100 grammes of gelatine (according to external temperature) and 

 dissolve. Boil for a few minutes, until all the casein is precipitated, 

 and pass through a fine muslin strainer. The fluid is allowed to 



