90 



BACTERIOLOGY. 



FIG. 15. 



sterilization to which they are to be subjected. At the 

 end of this time they are placed in previously prepared 

 test-tubes, one piece in each tube, with 

 the slanting surface up, the cotton plugs 

 of the tubes replaced, and they are then 

 to be sterilized iu the steam for forty- five 

 minutes. On the second and third days 

 they are to be sterilized for fifteen to 

 twenty minutes each day. 



Or the entire sterilization may be ac- 

 complished in the autoclave with the 

 steam under a pressure of one atmosphere, 

 by a single exposure of twenty to twenty- 

 five minutes. When finished they have 

 the appearance seen in Fig. 15, except 

 that there is no growth upon the surface 

 as is shown in the cut. 



For some purposes potatoes may be ad- 

 vantageously peeled, sliced into discs of 



potato iT^st-tube. about l c - m - in thickness, and placed in 

 small glass dishes provided with covers, 

 similar to the ordinary Petri dishes. The dish and its 

 contents are then sterilized by steam in the usual way 

 (method suggested by von Esmarch). By this plan a 

 relatively large area for cultivation is obtained. 



Potatoes may also be boiled, or steamed, and mashed, 

 and the mass placed in covered dishes, test-tubes, or 

 flasks, and sterilized. By this method one obtains in 

 the mass a mean of the composition of the several pota- 

 toes, or bits of potatoes, used in making it, an advantage 

 where uniformity is desired. 



Care must be given to the sterilization of potatoes, 

 because they always have adhering to them the organ- 



