58 BACTEIUOLOGY 



requires a certain amount of skill, and therefore Unna, 

 Fodor, and others have quite recently described contri- 

 vances for facilitating the operation. 



Roll cultures. — A modification of the plate process which 

 is known as roll culture has been invented by Von Esmarch, 

 in which the gelatine, after being liquefied and inociilated, 

 is kept rolling round the sides of a wide test-tube until it 

 sets. 



Eoll cultures are prepared by inoculating the tube in 

 the usual way, closing it with a cotton-wool plug which has 

 first been singed in the flame, and drawing over the cotton 

 an india-rubber cap sterilised in solution of corrosive subli- 

 mate. The tube is then seized by its upper end with three 

 fingers of the right hand and by its lower with three fingers 

 of the left, laid horizontally in a vessel of iced water, and 

 kept turning on its long axis until the gelatine has set in a 

 layer of even thickness. The roll cultures when finished 

 must at once be conveyed into a cool place. 



Modifications of tlie plate process. — A quicker and more 

 convenient procedure is the introduction of portions of the 

 gelatine into Petri's capsules. In using Soyka's plates a 

 small quantity of liquefied gelatine is deposited in each 

 hollow, and prepared with the seed-material by means of a 

 platinum needle. By transferring the material from one 

 hollow to another, it is possible to have all degrees of 

 attenuation on the same plate. 



In order to economise gelatine Giinther places on a 

 sterilised surface of glass a few drops of sterilised water or 

 bouillon, lying isolated from one another. A sample of the 

 material to be examined is mixed with the first drop by 

 means of the platinum wire, and by the same means the 

 inoculating matter is transferred to the remaining drops one 

 after the other, the needle being continually sterilised at 

 a red heat after each inoculation. From the last drop a 



