PREPARATION AND CARE OF CULTURE MEDIA. 99 
and other substances decompose at these high temperatures and the results 
obtained by the growth of bacteria in such media are not comparable with those 
obtained on media sterilized at 100°C. Hitchens has recently shown that detri- 
mental acids are formed when bouillon containing sugar is autoclaved. Peptone 
water, agar, and bouillon may be sterilized in the autoclave. For titrating culture 
media the writer uses the burettes shown in fig. 59. ‘The twentieth-normal alkali 
is stored as shown in fig. 60. Quadruple-normal sodium hydrate solution is used 
for neutralization. ‘The phenolphthalein solution is made by adding 1 gram of 
the dry powder to 100 cc. of 50 per cent alcohol, and then enough x sodium hydrate 
to carry it fully into solution, removing the yellow color without making the fluid 
a very decided pink. Fluid media may 
be filled into tubes very rapidly by means 
of the device shown in fig. 83. For storing 
media sterilized in test-tubes and for hold- 
ing cultures made on such media the writer 
has found ordinary quinine cans very use- 
ful (fig. 84). 
The proper care of culture media after 
sterilization involves considerable thought 
i | if they are not to be used immediately. 
| | 
Stored media lose water and along with 
this loss, of course, there are physical 
changes, so that the results obtained 
are not always comparable with those 
obtained from similar media containing 
the standard volume of water. Various 
devices have been recommended for pre- 
venting this loss of water. Rubber caps 
keep in the moisture, but are apt to 
favor the development of fungi. Paraf- 
fined plugs made by removing the cotton 
plug, dipping the lower end of it quickly into and out of hot sterile paraffin, and 
replacing it in the mouth of the tube or flask before the melted paraffin has had 
time to cool, answer the purpose very well, but have the objection that all of the 
tubes must be placed in turpentine or some other solvent of paraffin before they 
can be cleaned for a second use. On the whole, the use of moderately tight plugs 
and the storage of the media in cool or cold air are the best methods of retaining 
the water content of the medium. Nutrient media should be made in small quan- 
tities and often, rather than in large quantities and at infrequent intervals. ‘The 
cotton should be dry-heated in bulk before plugs are made from it. 
Fig. 84.* 
*Fic. 84.—Ordinary quinine cans with a little cotton in the bottom are very convenient for 
_ holding cultures and culture-media in test-tubes. One-third actual size. 
