100 BACTERIOLOGY. 



during collection of the serum are not so necessary, and 

 the resulting medium, while not transparent or even 

 translucent (points aimed at in the ^original method), 

 fully meets all the requirements. 



The special points in the method are: the serum is 

 decanted into test-tubes as soon as obtained; it is then 

 firmly coagulated in a slanting position in the dry-air 

 sterilizer at from 80 to 90 C.; it is then sterilized in 

 the steam sterilizer at 100 C. on three successive days, 

 as in the case of other culture media. It may then be 

 protected against evaporation by sterilized rubber caps 

 or sterilized corks in the way already described, and set 

 aside until needed. 



Unless the coagulation in the dry sterilizer be com- 

 plete, the surface of the serum will be found to be blis- 

 tered and pitted by bubbles and cavities after it has 

 been subjected to the steam sterilization. A similar 

 formation of cavities over the surface of the serum will 

 occur if the temperature of the hot-air sterilizer, in 

 which it is solidified, is allowed to get above 90 C., 

 or if it be elevated to this point too quickly. 



It is of no special advantage to have the serum clear, 

 as the admixture of blood-coloring-matter does not 

 affect its nutritive properties. 



It is often desirable to obtain blood-serum in small 

 quantities, either for culture purposes or for the study 

 of the serum of different animals in its relation to bac- 

 teria, and for this purpose Nuttall (Centralb. fur BaM. 

 u. Parasitenkunde, 1892, Bd. xi. p. 539) suggests a very 

 convenient method. By the use of a sterilized vessel, of 

 the shape given in Fig. 20, from ten to one hundred 

 cubic centimetres of blood can be collected, and if proper 

 precautions are observed no contamination by bacteria 



