17-1 PROCEEDINGS OF THE AMERICAN ACADEMY. 



action is caused by the first, a mould discovered on decaying paper, 

 though Mucor mucedo, which is more widespread than the first, is 

 only a little less active. The conditions for development of the com- 

 pound by these moulds are moisture, a temperature from 15 to 35° C. 

 (60-95° F.) and a supply of oxygen, without which no action takes 

 place. A large amount of arsenic retards the growth, which goes 

 on best in a ground containing 0.01 to 0.05%. The best nutritive 

 material is a carbohydrate. The development may take place in pres- 

 ence of arsenious oxide or its derivatives, or of arseniates, though the 

 latter seem to me to have given the best results. Little or no action 

 is obtained from the sulphides. 



As to the nature of the volatile compound it was thought from the 

 work of Hamberg and the speculations of others to be arseniuretted 

 hydrogen, an assumption that has been very misleading. Certainly 

 very little, and I think none, is formed. As far as the results go, the 

 compound seems to be a neutral organic derivative, and my opinion 

 is that the results favor its being an organic derivative of arsenic 

 pentoxide. No definite properties beyond its peculiar alliaceous odor 

 and volatility have been found, except that the yellow compound 

 noticed by Hamberg, Gosio, and myself may be a " molecular " com- 

 pound with argentic nitrate. 



It may be remarked in passing that the proof of the formation of a 

 volatile compound is a complete explanation of the poisoning in many 

 cases where an arsenical paper underlies one that is free from arsenic. 

 Also, though the effect of an arsenical paper may be temporarily 

 lessened by a varnish or size, that the danger is not removed. 



With the volatile compound we have to consider the question not 

 only of more minute doses than in the case of dust, but of a form 

 which permits the arsenic to enter the system more easily by the 

 lungs and in a state differing greatly from any dust. Whether we 

 have a derivative of arsenious or arsenic acid, the fact that the mole- 

 cule contains carbon is a very important one. 



The experiments of Schroter * on the poisonous action of p-benz- 

 arsenic acid, C 6 H 4 (C0 2 H) . AsO(OH) 2 , are interesting here, though 

 it is not likely that the volatile compound is an aromatic derivative. 

 Schroter found that the amount of arsenic in a fatal dose of benzar- 

 senic acid was somewhat larger than in a fatal dose of either arsenic 

 or arsenious acids, but that death followed after a much longer inter- 

 val than with either of the others. The early symptoms were refer- 

 able to benzoic acid, the later to arsenical poisoning. 



* Inaug. Dissert., Erlangen, 1881. 



