54 PRACTICAL BACTERIOLOGY. 



lipSj in order to ascertain whether it is sufficiently 

 cooled, it is certain to be re-impregnated with germs. 

 Even if, in the experiment in question, it does not 

 much matter if some species, not contained in the meat 

 infusion, develop at the same time, still it is of the 

 greatest importance to get into the habit of prevent- 

 ing the accidental introduction of foreign germs. 

 There is nothing which requires greater neatness and 

 care than bacteriological work, and the earlier the 

 operator accustoms himself to the most painstaking 

 cleanliness and care the more rarely will he have 

 failures, and the sooner will he become a successful 

 bacteriologist. 



It is of importance that the dishes should stand as 

 horizontally as possible after they have been filled ; on 

 this account it is best to place them on a glass plate, 

 which has been made absolutely horizontal beforehand. 

 This can be tested with a spirit level. According to 

 the temperature of the room the gelatine takes a, 

 longer or shorter time to solidify; after that has 

 occurred they can be placed in large glass dishes (see 

 Fig. 1), which have been previously sterilised with 

 corrosive sublimate solution. 



If it is desirable to make the cultivations in agar- 

 agar, the same method is adopted, only it is a good 

 thing to warm the dishes beforehand to about 40° C, 

 and above all to work very quickly, for the agar-agar 

 solidifies at a temperature of 40°-46° C, and after 



