THE EFFECT OF ANAEROBIC CONDITIONS 165 



A Kipp generator is connected up with three wash bottles, 

 containing: 



(a) 10% lead acetate solution to remove H^S ; 



(6) Silver nitrate solution to remove AsHs ; 



(c) 10% pyrogallic acid solution made alkaline to remove 

 any trace of oxygen, may be used to furnish hydrogen. 



Hydrogen is most conveniently obtained by keeping a 

 cylinder of the compressed gas in the laboratory. This 

 gas generally contains about 99.6% hydrogen, the remain- 

 ing 0.4% is mostly or entirely air, which represents 0.08% 

 oxygen. The gas so kept requires no preliminary washing, 

 but may be passed direct from the cylinder into the jar 

 or flask. 



Carbon dioxide is harmful to a large number of organ- 

 isms, as is also coal gas. Nitrogen is satisfactory, but its 

 method of preparation is so difficult that its use should be 

 abandoned in practical bacteriology unless it can be obtained 

 compressed in cylinders. 



EXERCISE 2. THE EFFECT OF ANAEROBIC CONDI- 

 TIONS UPON MICROORGANISMS FROM MANURE 



Apparatus. Modeling clay; tubes of sterile gelatin; 

 three sterile Petri dishes; three sterile deep-culture dishes 

 (use top of Petri dish for cover); sterile 1 c.c. pipettes; 

 sterile dilution flasks; six tubes of sterile agar; pyrogallic 

 acid; 10% solution of sodium hydrate; absorbent cotton. 



Culture. Horse manure. 



Method. 1. Plate the manure (1 gm. in 99 c.c. dilu- 

 tion flask) in duplicate in the Petri dishes and in the deep 

 culture dishes, using dilutions 1 : 100, 1 : 10,000 and 

 1 : 1,000,000. 



2. As soon as the agar is solid, invert the deep culture 

 dishes containing the dilutions. 



3. Place a small piece of absorbent cotton in the center 

 of the cover. This must not touch the agar. 



4. On the absorbent cotton, place 1 gm. of pyrogallic 



