7V) nRTKRMLVK THERMAL DKATH-PO/NT. 181 Easier of execution, but rather more severe, is a method in which cover-classes are employed. A num- ber of them are spread with cultures of various bacteria, allowed to dry, and then exposed to the gas as long as required. The cover-classes are afterward dropped into culture-media to permit the growth of the germs not destroyed. Animal-experiments may also be employed to deter- mine whether or not a germ that has survived exposure to the action of reagents has its pathogenic power destroyed. An excellent example of this is seen in the case of the anthrax bacillus, a virulent form of which will kill rab- bits, but after being grown in media containing an insufficient amount of a germicide to kill it will often lose its rabbit-killing power, though still able to fatally infect guinea-pigs, or may lose its virulence for both rabbits and guinea-pigs, though still able to kill white mice.