INOCULATING TUBES OF BOUILLON 15 



cup and place it in the incubator.^ This should be kept at a 

 temperature between 35 and 37° C. The organism thus trans- 

 ferred should multiply so that on the following day the liquid 

 will be cloudy. It is then a bouillon culture of B. colt com- 

 munis. 



20. Inoculating Tubes of Agar. — Ordinarily the agar is 

 inclined before it is inoculated. In this case it is spoken of as 

 inclined or slant agar. Occasionally the agar is inoculated 

 without inclining it. Cultures made in this manner are spoken 

 of as " stab " or " stick " cultures, (i) Inclined or slant agar. 

 Stand a tube of agar in a wire basket in a water bath and boil 

 it until the agar is liquefied. (To save repeating this it is well 

 to incUne the agar in several tubes which can be kept for future 

 use, but after the slants have been made for a long time it is 

 better to boil and reslant them, especially if they are to be used 

 for organisms which do not grow well on a dry surface.) Lay 

 the tubes on a tray, the top resting on the side of the tray so 

 that the surface of the agar will be about 4 cm. long, and allow 

 it to cool. In placing the tubes the label should be up. When 

 the agar has set, it is ready for use. It is inoculated precisely 

 as the bouillon, excepting the loopful of culture is drawn over 

 the inclined surface instead of being thrust into the medium 

 as in the bouillon. Label and place it in the incubator with 

 the inoculated bouillon tube. On the following day there 

 should be a grayish white growth on the surface of the agar 

 covered by the loop. This is an agar culture of B. coli com- 

 munis. (2) Stick cultures. These are made with a platinum 

 needle in the uninclined agar. The impregnated needle is 

 pushed down through the centre of the agar. In all other 

 respects this culture is made like the slant agar culture. 



^ For illustrations and descriptions of different kinds of incubators, see 

 text-books. It is desirable to note especially the various burners and 

 thermo-regulators employed to heat and to regulate the temperature of the 

 incubators. Considerable information can also be acquired by carefully 

 looking through the catalogues of manufacturers and dealers in bacteriologic 

 apparatus. Copies of some of these will be found on the reference book 

 shelves. 



