^8 PHARMACEUTICAL BACTERIOLOGY. 



just high enough to keep the contents liquid; set them in a beaker filled 

 with warm water (30° C.) until needed. Number the tubes from i to 5. 

 Dip a platinum loop (bend the end of a straight needle into a small loop) 

 into the infected liquid, as bouiUon, milk, water, tea, syrup, tincture, fluid- 

 extract, etc., etc., and pass one loopful into tube No. i (sterilize loop and 

 return to its proper place) . Rotate tube (replugged with the cotton and held 

 vertically) rapidly between the hands for twenty seconds, to mix contents. 

 By means of the platinum loop take two loopfuls (one loopful may serve) 

 from tube No. i (which you have just inoculated and rotated) and pass 

 them into tube No. 2. Plug both tubes, set aside tube No. i, and rapidly 

 rotate tube No. 2. Take two loopfuls from tube No. 2 and transfer to tube 

 No. 3, and proceed as before. Now pour contents of tube No. i into a sterile 



Fig. 35. — ^Appearance of colonies on gelatin in a Petri dish. Differences in size of 

 colonies may indicate different species. Differences in color also indicating different 

 species, cannot be shown in the figure. {Williams.) 



Petri dish, also numbered i; contents of tube 2 into Petri dish 2; and tube 

 3 into Petri dish 3. Wait until the media in the Petri dishes are solidified, 

 and then set aside at the room temperature to await developments. In the 

 course of two or three days it will perhaps be found that very many minute 

 specks are visible in dish No. i, some one hundred or more may appear in 

 dish No. 2, and perhaps not more than ten or twenty in dish No. 3. Observe 

 carefully the several growths in dishes 2 and 3. Each visible growth in- 

 dicates the development from a single microbe. Are the several growths 

 all alike, or do they differ? Differences in color and in outline of growths 

 indicate different species of bacteria. The several different kinds of bacteria 



