﻿338 The Philippine Journal of Science i9u 



light or artificial light may be used, but a fairly strong illumina- 

 tion is advisable, especially when the higher powers are used. 

 The oil immersion can be readily used over the isolating chamber 

 without resorting to any special illumination. 



PIPETTES 



Pipettes may be made some time before use and kept in a 

 sterile chamber or placed in a sterile test tube or flask with 

 the shank held in place by the cotton plug, somewhat as shown 

 in fig. 16. It is usually more convenient, however, to make the 

 pipette just before use. A very convenient plan is to close the 

 pieces of glass tubing intended for pipettes at one end with 

 cotton and to draw them out into a coarse capillary at the 

 other. The capillary is sealed at the tip, and the pipette steril- 

 ized in the hot-air sterilizer. A number may be sterilized 

 and kept in stock ready for use. The coarse capillary may be 

 drawn out and made into a tip for isolating, or may be simply 

 turned up in the Bunsen flame and broken off for use in placing 

 the preliminary drops of sterile liquid or solid media on the 

 cover. 



GAS FOR THE MICROBURNER 



When natural gas is used, it is sometimes difficult to keep 

 the small flame lighted. This can be remedied by causing the 

 gas to pass through a bottle containing benzine or other en- 

 riching fluid. 



SPECIAL APPLICATIONS OP THE PIPETTE METHOD 



ISOLATION OF ORGANISMS FROM QUANTITIES OF WATER LARGER THAN 



HANGING DROPS 



Sometimes it is desirable to isolate algae, protozoa, bacteria, 

 or other organisms from water or from a culture in which 

 they occur in such small numbers that one cannot find them 

 readily in the hanging drop. In this case, a Petri dish, a watch 

 glass, or other receptacle containing the organisms may be placed 

 on the stage of the microscope and a pipette, bent as shown 

 in fig. 13, may be adjusted in the holder. The capillary need 

 be bent only enough to avoid the edge of the dish. The point 

 of the pipette is made as fine as desired, the opening being suited 

 to the size of the microorganism. The tip is bent down obliquely, 

 if the organisms sought are likely to be at the bottom ; or bent 

 upward, if they are to be sought at the surface. It is possible 

 to scrape the bottom with the pipette and loosen and take up 

 any adhering amoebae or spores of algae. When the organism 

 sought is taken into the pipette, the tip is raised above the surface 

 of the water, the Petri dish removed, and an ordinary isolating 



