Here his research focused on testing arsenical dyes for killing microbes. Caesium salts have been evaluated as antishock reagents following the administration of arsenical drugs. Outbreaks can be treated with an arsenical spray. Common laborers only had arsenical copper objects. This innovation resulted in the circulation of arsenical bronze technology over southern and eastern Europe. At the Rockefeller Institute, Simon Flexner organized a group to test arsenical compounds. The ArsD family consists of several bacterial arsenical resistance operon trans-acting repressor ArsD proteins. Melamine derivatives of arsenical drugs are potentially important in the treatment of African trypanosomiasis. Lead arsenate was the most extensively used arsenical insecticide. Arsenical bronze has seen little use in the modern period. Poultry feed can include roxarsone or nitarsone, arsenical antimicrobial drugs that also promote growth. Organic chickens not exposed to arsenical feed additives contained about half a part per billion. The autopsy of Michael Collins declared the cause of death to be "arsenical poisoning". Arsenical bronze was used by many societies and cultures across the globe. Some arsenical compounds are shown to treat the trophozoite stage, like carbarsone.