270 BACTERIOLOGICAL METHODS 



volatile substances having the garlic-like odor. The following 

 procedure is recommended. 



If the material to be examined is liquid, let the dry bread 

 crumbs (either white or graham) absorb it to saturation, and 

 then scatter a small quantity of fine crumbs over the surface. If 

 the material to be tested is solid, grind or cut it into small pieces 

 and mix with an equal amount of the bread crumbs and then 

 moisten with a little sterile distilled water. Place the prepared 

 material in sterile flasks of suitable size and plug with sterile 

 cotton. Sterilize the flask and contents by the usual fractional 

 method at 100 C., or for 30 min. in the autoclave. Absolute 

 sterilization must be secured. There is no danger of volatilizing 

 the arsenic at these temperatures. As soon as flask and contents 

 are cold, inoculate with the mold, as follows. The mold cultures 

 may be grown on bread or on pieces of potato. Remove a small 

 quantity of the mold in the spore-forming stage and mix with 

 peptone salt solution or sterilized water. Add enough of this 

 mold suspension to just moisten the bread in the flask. Do not 

 add more of the spore-bearing material than the mass (bread and 

 arsenical substance) in the flask will absorb as too much moisture 

 will retard growth. Cover the inoculated flask with a rubber cap 

 and incubate at a temperature of 37 C., although the ordinary 

 room temperature will answer the purpose. As soon as the growth 

 is clearly visible to the naked eye, which may be in 24 hr., the char- 

 acteristic garlic odor will be noticed upon opening the flask. If 

 no odor is appreciable, again seal and incubate for another 24 hr. 

 period or even longer. In case the substances to be tested are 

 strongly acid, they may first be neutralized by means of calcium 

 carbonate. It must also be kept in mind that Penicillium brevi- 

 caule, as well as other molds, will convert tellurium and selenium 

 compounds into volatile substances having a garlic-like odor. The 

 arsenic and tellurium odors are very closely similar but that from 

 selenium is somewhat different in quality, more like that of mer- 

 captan. The test is extremely delicate, o.ooooi gram of arsenic 



