168 LABORATORY METHODS OF 



placing it on the top side of a cover-slip and turning 

 the cover-slip down 'on the slide and watching the mo- 

 tion or non-motion of the germ. 



COIyONY COUNTING. 



1. Take a Petri dish and divide it off into equal seg- 

 ments and place it on the table, with a black surface 

 under the dish. 



2. Take I c.c. of the fluid to be used and carefully 

 mix it with a tube of gelatine. 



3. Pour the contents of the tube into the dish. 



4. Incubate twenty-four hours at the room temper- 

 ature. 



5. With the aid of a lens count the colonies that ap- 

 pear in the dish. (Each colony represents a bacterium 

 to begin with.) 



BACTERIOLOGICAL EXAMINATION OF THE BLOOD. 



1. Sterilise the part carefully with 1-1,000 perchlo- 

 ride of mercury ; then wash off the mercury with alcu- 

 hol; let the alcohol evaporate; wipe the part with a 

 dry sterile cloth or absorbent cotton. 



2. Prick the part with a needle prepared for the 

 purpose by sterilising with dull heat. 



3. Take a loop of the blood from the part and put 

 it in the media, and if you get a growth, make the 

 whole test for bacteria as directed further on. 



