PETRPS CAPSULES. 63 



gelatine from a to b. Shake b and transfer two loops to c. 

 The plugs of the tubes are in each case replaced and the 

 tubes returned to the beaker. The contents of the three 

 tubes are then poured out into three capsules. In doing 

 so the plug of each tube is removed and the mouth of the 

 tube passed two or three times through the Bunsen flame, 

 the tube being meantime rotated round a longitudinal axis. 

 Any organisms on its rim are thus killed. The capsules 

 are labelled and set aside till growth takes place. 



The colonies appear as minute rounded points, whitish 

 or variously coloured. Their characters can be more 

 minutely studied by means of a hand-lens or by inverting 

 the capsule on the stage of a microscope and examining 

 with a low power through the bottom. From their charac- 

 ters, colour, shape, contour, appearance of surface, lique- 

 faction or non- liquefaction of the gelatine, etc., the colonies 

 can be classified into groups. Further aid in the grouping 

 of the varieties is obtained by making film preparations 

 and examining them microscopically. Gelatine or agar 

 tubes may then be inoculated from a colony of each variety, 

 and the growths obtained are then examined both as to 

 their purity and as to their special characters, with a view 

 to their identification (p. 123). 



2. Glass Plates (Koch). When plates of glass are to be 

 used, an apparatus on which they may be kept level while 

 the medium is solidifying is, as has been said, necessary. 

 An apparatus devised by Koch is used (Figs. 18, 19). This 

 consists of a circular plate of glass (with the upper surface 

 ground, the lower polished) on which the plate used for 

 pouring out the medium is placed. The latter is protected 

 from the air during solidification by a bell jar. The 

 circular plate and bell jar rest on the flat rim of a circular 

 glass trough, which is fil ! ed quite full with a mixture of ice 

 and water to facilitate the lowering of the temperature of 

 whatever is placed beneath the bell jar. The glass trough 

 rests on corks on the bottom of a large circular trough, 

 which catches any water that may be spilled. This 

 trough in turn rests on a wooden triangle with a foot at 



