CULTURES, AND THEIR STUDY. 125 



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 6n 

 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 " klatsch 

 praparat. ' ' 



The development of bacteria in liquids is of less in- 

 terest than that upon solid media. The growth generally 

 manifests itself by a diffuse turbidity. Sometimes flocculi 

 float in the otherwise clear medium. Some forms grow 

 most rapidly at the surface of the liquid, and produce a 



