66 METHODS OF CULTIVATION OF BACTERIA 



passing through the glass tubes, washes out the potash and 

 prevents erosion of the glass. The whole apparatus may be 

 placed in the incubator till growth occurs. 



(c) Lentz's Method. The requisites for this are glass plates, 

 discs composed of layers of filter paper compressed together and 

 impregnated with pyrogallol (obtainable from Lautenschlager, 

 Berlin), 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. 



McLeod has modified this method in the following way. 

 Instead of glass plates he uses shallow circular porcelain capsules l 



L JJ 



FIG. 23. McLeod's capsule for anaerobic plating, shown in section. 



(Fig. 23, a) which are covered in by a porcelain diaphragm with 

 the exception of a circular opening in the middle. The interior 

 of each capsule is divided into two halves by a partition which, 

 however, does not extend the whole way up ; in one half, solution 

 of pyrogallic acid is placed, in the other, solution of potassium 

 hydrate. Plasticine is placed round the margin of the upper surface 

 of each capsule. Plate cultures having been made in glass dishes 

 in the usual way, each dish is inverted and placed over a porcelain 

 capsule and carefully fixed in the plasticine. When this has been 

 done, the two fluids in the capsule are mixed by tilting and the 

 oxygen in the interior is rapidly absorbed. Another improvement 

 is that the edges of the glass dishes which rest in the plasticine are 

 turned up so as to prevent the condensation water from running 

 over the plasticine (Fig. 23, b). 



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

 Hamilton, Glasgow. 



