156 



BIOLOGY AND TECHNIQUE 



larger, and placed, still inverted, over a moist surface a towel or the 

 wet surface of the table to prevent contamination. Into the bottom 

 of the larger dish, which now stands open, there is placed a quantity 

 (about 3 grams) of dry pyrogallic acid. Into this, over the pyrogallic 

 acid, the smaller dish, still inverted, is then placed. A five per cent solu- 

 tion of sodium hydrate is poured into the space left between the sides of 

 the two dishes, in quantity sufficient to fill the receiving dish one-half 

 full. While this is gradually dissolving the pyrogallic acid, albolin, 

 or any other oil (and this is the only step that requires speed), is 

 dropped from a pipette, previously filled and placed in readiness, into 



FIG. 40. SIMPLE APPARATUS FOR PLATE CULTIVATION OF ANAEROBIC BACTERIA. 



(Zinsser.) 



the same space, thus completely sealing the chamber formed by the two 

 dishes. 



If these steps have been performed successfully, the pyrogallic solu- 

 tion will at this time appear of a light brown color, and the smaller plate, 

 with its agar film, will float unsteadily above the other. Very rapidly, 

 as the pyrogallic acid absorbs the free oxygen in the chamber, this plate 

 is drawn down close to the other, and the acid assumes a darker hue, 

 which remains without further deepening even after three or four days' 

 incubation. 



The Use of Fresh Sterile Tissue as an Aid to Anaerobic Cultivation. 

 The addition of small pieces of fresh sterile tissue (rabbit or guinea- 

 pig) to culture tubes, either solid or fluid, greatly favors the growth of 

 anaerobic bacteria. By such a method anaerobes can be made to de- 

 velop even when other precautions for the establishment of anaerobiosis 



