CULTURES, AND THEIR STUDY. 147 is removed cautiously ; the wire bearing the bacteria from the colony is introduced until its point enters the centre of the gelatin, and is then carefully pushed on until a vertical puncture from the surface to the bottom of the gelatin is made. This is the puncture-culture— u stichcultur " of the Germans. If the bacteria are only to be planted upon the surface of the culture-medium, the wire is drawn over the surface of a tube of obliquely solidified gelatin, agar-agar, blood- serum, etc. with a steady, slow movement, so as to scatter the germs along its path and cause the development of the bacteria in an enormous colony or mass of colonies in a line following the longest diameter of the exposed surface from end to end. This is the stroke-culture— u strichcultur." The method of holding the tubes, cotton plugs, and platinum wire during the process of inoculation is shown in Figure 20. Sometimes it is desirable to preserve an entire colored colony as a microscopic specimen. To do this a perfectly clean cover-glass, not too large in size, is momentarily warmed, then carefully laid upon the surface of the gelatin or agar-agar containing the colonies. Sufficient pressure is applied to the surface of the glass to exclude bubbles underneath, but the pressure must not be too great, as it may destroy the integrity of the colony. The cover is gently raised by one edge, and if successful the whole colony or a number of colonies, as the case may be, will be found adhering to it. It is treated exactly as any other cover-glass preparation, is dried, fixed, stained, and mounted, and kept as a permanent specimen. It is called an adhesion preparation—u klatsch praparat.'' Very often, when one is in a hurry, pure cultures from single colonies may be secured by a very simple manipu- lation suggested by Baiiti.1 The inoculation is made into the water of condensation at the bottom of an agar- 1 Centralbl, f. Bakt. imd Parasitenk.y 1895, xvii., No. 16.