TEXT-BOOK OF BACTERIOLOGY. 97 



take out a plate, and lay it on the cool surface of the glass plate 

 covering the iced water. A bell-glass prevents germs from faUing 

 upon it from the air. Next take the first test-tube, slant it a few 

 times up and down, to distribute the germs as thoroughly as possi- 

 ble in the liquid, remove the cotton plug with a pair of forceps, 

 raise the bell-glass, and pour the gelatin over the plate, aiding its 

 distribution by means of the edge of the test-tube. 



Under the protection of the bell-glass, which is immediately re- 

 placed, the gelatin consolidates in a few minutes. It should be 

 evenly spread in a thin, uniform layer over the surface, stopping 

 within about 2 cm. of the edge on all sides. 



The prepared plate is now removed and placed in a moist cham- 

 ber, to prevent it from drying up. Spread some blotting-paper 

 over the bottom of a glass dish (as in the potato cultures), moisten 

 it slightly with water, and place the plate preparation upon it. It 

 is desirable, for the sake of convenience, to put several — say half a 

 dozen— such plates together in one dish, one above another, sepa- 

 rated by little glass bridges or benches. Each of these bridges 

 should, of course, be labelled with name, source, and date. In the 

 present case, for instance, " II., VII., Faeces, O." ( February 7th, Fseces, 

 Original); then follows the glass plate; next immediately over it a 

 " bridge " with its label, " II., VII., Faeces, I." (February 7th, Fajces, 

 1st dilution) ; then the second glass bridge, etc., etc. It is not neces- 

 sary to sterilize the glass bridges, as they do not come into contact 

 with the gelatin and have therefore no opportunity to pollute it. 



Keep the bell-glasses in a moderate!}' warm place, and await 

 the development of the germs in the shape of colonies. 



The original glass-plate process of Koch which has just been 

 explained has within a few years conquered the world, so to speak, 

 and found its way into every laboratory. In fact, its advantages 

 over the former methods are so evident and its manipulation is 

 so simple that in this respect hardly anj'thing seems left to im- 

 prove upon. And yet it has its disadvantages. The most seri- 

 ous one is, perhaps, that it can onlj' be conducted in a laboratory, 

 since it requires a certain amount of space and certain special 

 apparatus. 



It is true we may do without the latter in case of need; the 

 test-tubes and glass plates can be sterilized in an open flame, the 

 plates can be laid on the level surface of a table, and the gelatin 

 poured over them there, etc., etc. But then there remains the pro- 

 tection of the finished preparations from drying up and from being 

 polluted. This requires space, transportation is almost impossible, 

 and investigation during a journej', a campaign, etc., is extremely 

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