Abstract
The blood and urine of mice and rats infected with Babesia rodhaini contain substances which stimulate the isolated guinea-pig ileum and rat duodenum. The amount of active material excreted increases as the infection increases. The active substances are stable to boiling with hydrochloric acid but not with alkali; they pass through a cellophane membrane and are soluble in hot ethanol. They are destroyed rapidly by papain and less rapidly by chymotrypsin, but are unaffected by trypsin or pepsin. Their action on smooth muscle is not affected by atropine, eserine, antihistamines, iproniazid, bretylium or by lysergic acid diethylamide. The active substances are probably peptides and there is evidence that the urine contains a mixture of peptides, some of which relax and some of which contract the rat duodenum. Similar active peptides appear in the urine of mice infected with Plasmodium berghei, Trypanosoma rhodesiense, Streptococcus pyogenes and Rift Valley fever virus.