74 CULTURES AND THEIR STUDY. 



After it has solidified it is inoculated. When the growth has 

 developed sufficiently, the entire block is sectioned under 

 alcohol and the sections are stained with a weak carbol-fuchsin 

 solution. 



On media having a slanting surface, such as agar, potato, 

 or blood-serum, a stroke or smear culture is made. For a 

 stroke, the wire is passed in a straight line across the centre 

 of the surface; for a smear, the needle is rubbed gently over 

 the entire surface. In neither case does the needle penetrate 

 the medium. 



The comportment of the germ toward oxygen is noted also. 

 A heavy surface growth denotes aerobic tendencies. A 

 heavy growth along the line of inoculation and a slight sur- 

 face growth denote anaerobic tendencies. 



These tubes are incubated and a record of the growth made 

 from time to time. Gelatin tubes and dish cultures cannot 

 be placed in the incubator because of the low melting-point 

 of the gelatin. For this reason agar is used mostly in the 

 preparation of the dish cultures. 



FIG. 28. 



,"^>' ^--V^'-r^K" ' 



fc^C^^^^r^vv 



ij^t^^sSv 

 $&^i$ig$/ 



Zoogtoa of bacilli. (Abbott.) 



The membranous pellicle formed by bacteria on the surface 

 of liquid media is called a mycoderma. When the growth 

 forms principally in the mass or body of the medium, gelati- 

 nous-looking masses are formed, the zooglcea (Fig. 28). 



Klatsch preparation : Occasionally it is desirable to make 

 a microscopic specimen of an entire colony. Take a clean 

 cover-glass, warm it slightly, and lay it 'carefully on the 

 colony. A little pressure will remove the air bubbles under 

 the cover-glass without destroying the contour of the colony. 

 The cover-glass is then lifted up carefully, when the colony 



