78 APPLIED BACTERIOLOGY 



anaerobic bacteria is that devised by Buchner, who 

 abstracts the oxygen from the air by means of pyrogalHc 

 acid and caustic potash. All that is necessary is to enclose 

 the inoculated culture-tubes in a larger tube, provided with 

 a closely-fitting and well-greased rubber stopper. Into the 

 bottom of the larger tube from a quarter to half an ounce 

 of pyrogallic acid is first introduced ; then, immediately 

 before closing it, a few c.c. of 10 per cent, caustic potash 

 solution is poured in by means of a funnel. In a short time 

 an atmosphere practically free from oxygen is produced in 

 the apparatus, and one in which strict anaerobes will give 

 evidence of good surface growths. Greater certainty may 

 be attained by the addition of 0"5 per cent, of sodium 

 formate to the culture medium. We have had no difficulty 

 in obtaining even good plate cultures of anaerobic bacteria 

 by this means. 



Hanging-drop Cultures. — With a platinum loop, a drop 

 of sterile broth is placed on a clean cover-glass which has 

 been passed through a flame. This drop is then inoculated 

 with a very minute trace of the organism under examina- 

 tion. A ' hollow ' slide is then taken — that is, one with a 

 concave excavation ground in the centre. The outside of 

 the well is then painted round with a narrow ring of 

 vaseline by means of a camel-hair brush ; the cover-glass, 

 with the drop of broth, is inverted and laid on the pre- 

 pared slide, and gently pressed down in such a way as to 

 make the cover-glass adhere firmly to the glass slide, so as 

 to make an air-tight joint, and thus prevent the drying up 

 of the drop by evaporation. 



The slide is then examined under the microscope — first 

 with a low power to find the edge of the drop, and then 

 with the higher powers, since, as it appears bounded by a 

 sharp line, the organisms in the drop can be more sharply 

 focussed. The narrowest possible aperture of the diaphragm 



