54 BACTERIOLOGY 



organisms deposited from the air in different places, or have 

 had a linear inoculation made on the surface. These 

 slide cultures are less in use at the present time, since, 

 in order to isolate the germs, a large surface must be given 

 to the nutrient medium, and consequently glass plates are 

 employed. Moreover, Koch has devised an exceedingly 

 ingenious method known under the name of the plate 

 process. 



Koch's plate process. Gelatine is stored in sterilised 

 test-tubes, plugged with cotton, to the amount of about 

 10 c. cm. in each, and is completely sterilised by the 

 fractional method. A pure culture, or a mixture of many 

 micro-organisms in a mass of any desired size having been 

 obtained, the gelatine in three test-tubes is liquefied in the 

 water-bath at a temperature of 35 C., and a small quantity 

 of the mass to be examined is taken on a platinum needle 

 (previously sterilised at a red heat) and introduced into the 

 first test-tube. The platinum needle may be bent round 

 into a circular loop at the end or have its point somewhat 

 flattened out. If the seed mass is rather too coherent, 

 attempts must be made to separate the micro-organisms by 

 rubbing them with the point of the needle against the side 

 of the test-tube below the surface of the gelatine. The 

 platinum needle having been again heated, three samples 

 are transferred with it from the first tube to the second, 

 and the same procedure is repeated with the second and 

 third, so that we have three inoculations, of which the third 

 is the most diluted. When inoculating care must be taken 

 in opening the tube to seize the plug of cotton-wool between 

 the fingers, best between the third and fourth, on the back 

 of the hand, and thus twist it out of the tube, which must 

 again be carefully closed after inoculation without allowing 

 the cotton plug to come in contact with the surface of the 

 hand or with any instrument. 



