64 METHODS OF CULTIVATION OF BACTERIA 



palladium chloride (to which a little hydrochloric acid may be added 

 if necessary), moulded into a flat cake and slowly dried. The palladium 

 chloride is reduced by heating the dried wool pledget in a smoky gas 

 flame till it is coated with carbon and then burning in a blowpipe. The 

 wool is then folded into the gauze capsule, which should be of just 

 sufficient size to enclose it. The lid being thus prepared, the culture 

 tubes are placed in the bottle. The capsule is heated in a Bunsen, and 

 the lid, with the tap closed, is rapidly fixed on the jar. The tap is 

 opened and a piece of pressure tubing leading from a hydrogen generator 

 is connected with it. The hydrogen is turned on, and combines with the 

 oxygen in the vessel till no free oxygen remains. At the end of the 

 process the internal pressure prevents the further entry of hydrogen. 

 The jar is allowed to cool, the tap shut off and disconnected from the 

 hydrogen supply, and the apparatus can then be incubated. It is 

 absolutely necessary that the lid of the jar should be airtight. This 

 can be tested by placing a few drops of ether in the jar, fixing on the 



Fig. 19. — Lid of M'Intosh and Fildes anaerobic jar. 1 



lid, and plunging the vessel in hot water ; any leak can thereby be 

 detected. A fitting similar to above can be adapted to any tin vessel 

 with a "lever-off" lid. In this case the lid is luted on with plasticine. 



Lentz's Method. — The requisites for this are glass plates, discs com- 

 posed of layers of filter paper compressed together and impregnated with 

 pyrogallol, some circular glass dishes of the form of the halves of a Petri 

 capsule. Plate cultures are prepared in the glass dishes in the usual way 

 and the medium is allowed to solidify. A disc is placed on a glass plate 

 and moistened with a potassium hydrate solution ; a dish is then rapidly 

 inverted over it and luted on the glass plate with plasticine. The other 

 dishes are treated in a similar way. 



M'Leod has modified this method in the following way. Instead of 

 glass plates he uses shallow circular porcelain capsules 2 (Fig. 20) which 

 are covered in by a porcelain diaphragm with the exception of a circular 



i For the use of this figure we are indebted to the National Insurance 

 Medical Research Committee, in whose Special Report, No. 12 (1917), the 

 apparatus is described. 



2 The capsules may be obtained from Messrs. Thomson, Skinner, & 

 Hamilton, Glasgow. 



