_D._ For slope or plate, or any type of surface cultures the Novy jar (Fig. 127) is the most practical device. It is good practice to combine the vacuum method, the hydrogen replacement method and the oxygen absorption method in using these jars. In operation a solution of 20 per cent. NaOH is poured on the bottom of the jar to a depth of 1 or 2 cm., the cultures are placed on glass supports above the alkali and a short wide tube of strong pyrogallol is set in on the bottom in such a way that it may be easily upset and mixed with the alkali when it is desired to do so. The cover is now clamped in position with all joints well vaselined. Then the outlet tube is connected with a suction pump and the air drawn out. Meanwhile the inlet tube has been connected with a hydrogen generator, and after the jar is exhausted hydrogen is allowed to flow in, and this process is repeated until one is satisfied that the air is replaced. The suction exhausts the air from the tubes or plates so that much less time is required to replace the air with hydrogen. Finally the stop-cock is closed, and the pyrogallol solution is gently shaken down and mixed with the alkali so that any remaining oxygen will be absorbed. [Illustration: FIG. 127.--Novy jars.] It must be remembered that facultative anaërobes as well as anaërobes will grow under any of the above conditions, so that cultures of organisms so obtained must be further tested aërobically in order to determine to which group the organisms belong. Reference has been made above to the “inoculation” of culture media, which means introducing into the medium used the desired material in the proper way. For small quantities this is most conveniently done with platinum “needles,” that is, pieces of platinum wire inserted into the ends of glass rods. The “straight” needle is a piece of heavy platinum wire of about 0.022 inch in diameter (Fig. 128). It is used most frequently to inoculate all forms of _solid media_. The platinum loop is of lighter wire, 0.018 inch. The loop in the end is conveniently made by twisting the wire around the lead of an ordinary lead-pencil. The “loop needle” (Fig. 129) is most used in transferring liquid media. On account of the high price of platinum, the author has substituted “nichrome” wire for student use. This is stiffer, not so easily made into loops and breaks out of the rods more easily. The latter defect is remedied to some extent, by imbedding the wire only slightly for about one-fourth of an inch on the side of the end portion of the rod. The low cost, less than one-twentieth of platinum, justifies its use. [Illustration: FIG. 128.--Straight needle.] [Illustration: FIG. 129.--Straight and loop needles.] [Illustration: FIG. 130.--Pasteur flask--“ballon pipette.”]