IOO BACTERIOLOGICAL LABORATORY TECHNIC 



A serum coagulating apparatus is needed in laboratories in order 

 to coagulate the tubes of blood serum. (Fig. 26.) 



Serum tubes are coagulated in it at a temperature of about 70 C. 

 They are then sterilized by heating them for an hour at this tem- 

 perature, for five successive days. 



The separation of bacteria from the bouillon in which they grow 



FIG. 26. Blood serum coagulating apparatus. 



for the preparation of toxins requires the use of a bacteria or germ 

 proof filter, the best type of which is the Chamberland or Pasteur 

 unglazed porcelain filter. These filters are of varying grades of 

 fineness, and are so made as to be easily sterilized. The common 

 pathogenic bacteria cannot pass through the pores of the ordinary 

 filter, but toxic agents are known to pass through the finest filters, 

 though they cannot be discovered, as they are submicroscopic. 



To operate the porcelain filter it must fit into the neck of a vessel 

 very tightly, so that a vacuum may be maintained in the latter by 

 means of an air pump. 



Collodion sacs are sometimes used in animal experiments. Bouil- 

 lon cultures are placed within the sacs, which are then inserted in 

 the abdomen of an animal and left there. The sac is made of 

 collodion because it is non-absorbent and allows the bacterial juices 



