CULTIVATIONS AT HIGHER TEMPERATURES. 87 



after the agar-agar has been poured into the dishes to 

 fasten them in with a few drops of the medium. This 

 is managed as follows. The round piece of blotting 

 paper, which should be just a little smaller than the 

 inner surface of the cover, and which has been steril- 

 ised in the dish, is left in the cover, whilst the dish is 

 held upside-down. The under dish is now lifted out, 

 all the agar-agar is poured in, except a few drops, 

 which are poured upon the blotting paper. Thfese 

 few drops soon solidify, and fasten the blotting paper, 

 as a rule, firmly to the cover, which is held during the 

 short time over the dish containing the agar-agar, in 

 order to prevent germs from the air falling in. The 

 whole operation requires some practice, but when 

 rightly done, is very successful, and quite answers the 

 purpose of rendering the condensation of the water 

 vapour harmless. By degrees the blotting paper 

 becomes saturated with moisture, when it clings all 

 the more firmly to the lid. It could never happen that 

 water would drop down from the paper to the agar- 

 agar, for the former is capable of absorbing more water 

 than the latter can give o£E. Especial care must be 

 taken that no impurities should occur in these plate 

 cultures, as in that case they would inevitably be 

 spoiled, since at these higher temperatures the sapro- 

 phytic bacteria grow so rapidly that they would soon 

 take possession of the whole dish. 



For the same reason the student is recommended to 



