THE COLLECTION AND EXAMINATION OF PUS 149 



-lower surface. Place it on a flat table to set. Repeat the pro- 

 cess with the other tubes. Incubate at about 20 C. for two or 

 three days. Examine the dishes, placing them on the stage of 

 the microscope and using the low power. Each organism will 

 have grown into a small colony, which will resemble those 

 which are described in the section on the blood. There will 

 be slight differences, but not enough to lead to error if the 

 examination of the colonies is supplemented by an inspection 

 of stained films. 



The pneumococcus, gonococcus, the fungus of actinomyces, 

 and the tubercle bacillus, will not grow on these plates; the 

 streptococcus and the bacillus of glanders will grow feebly, if 

 at all. 



In a day or two longer the plates will, in some cases, be 

 found to have undergone a decided change. If liquefying' 

 organisms are present the colonies will soon become de- 

 pressed below the general surface of the medium, and will be 

 surrounded by haloes which consist of liquefied g'elatin. This 

 will happen with the staphylococci and the B. pyocyaneus; 

 not with the streptococci, the typhoid bacillus, nor with the 

 B. coli. 



The bacillus of blue pus can readily be distinguished from 

 the staphylococci by its morphological appearance (it is a 

 slender rod), and by the fact that the gelatin round the colony 

 is coloured blue or bluish-green, the growth itself being nearly 

 white. 



Material containing a mixture of bacteria can also be separ- 

 ated very simply by making tube-plates on agar, selecting for 

 the purpose sloped tubes containing a g'ood amount of water 

 of condensation in each; old dry tubes are useless for the pur- 

 pose. Place a drop of pus on the surface, and with a platinum 

 loop smear it over the medium, .and at the same time tilt the 

 tube so that the water of condensation mixes with the pus, and 

 also flows over the surface. Take a loopful of this water of 

 condensation, and repeat the process in a second tube, pro- 

 ceeding* just as you did with the drop of pus in the first, and 

 in a similar way inoculate the third tube from the second. Put 

 the tubes upright, so that the excess of fluid may drain off the 

 upper part of the slope. One of the cultures will (after incu- 

 bation) probably show separate colonies, from which pure 

 subcultures can be made. 



