152 THE AMERICAN MONTHLY [May 



must be taken not to boil gelatin too long or it will lose 

 its property of solidifying when cold. 



Sterilization of Media. It will be seen that the pro- 

 cess of preparing culture media up to the point of steril- 

 ization is practically the same as that described in recent 

 text books on bacteriology. The method is short and by 

 having the nutritive medium prepared and kept in stock 

 the preparation up to this point of either agar or gelatin 

 is very simple. The essential time consuming part of 

 the process is the sterilization. Although this has now 

 been reduced from the l)oiling on six consecutive days to 

 three, it is still an important element in laboratory work 

 especially where students are present but two or three 

 days, usually alternating, in each week. 



During the past two terms I have made a considerable 

 number of experiments for the purpose of determining 

 if it is necessary in order to secure complete sterilization 

 to boil media, when distributed in small quantities in 

 tubes, for three consecutive days. In these experiments 

 I have found that one boiling for a slightly longer time, 

 thirty minutes, seems to be all that is necessary to ster- 

 ilize bouillon, nutrient agar and nutrient gelatin distrib- 

 uted in either small or large tubes. After distributing 

 the medium the tubes were put in a closed water bath 

 and boiled vigorously for thirty minutes. At the expir- 

 ation of that time they were taken out and placed in an 

 incubator where they were allowed to remain for several 

 days, when it was a simple matter to sort out and reject 

 any tubes that may have been contaminated. As will 

 be seen from the appended tables, giving the results of 

 these experiments, contaminations have been very rare. 

 In fact they have not been much if any more numerous 

 than they were when the three regular boilings were em- 

 ployed. Although several of the agar and gelatin tubes 

 were not sterilized, they were contaminated with a spore 



