In recent years the reticulo-endothelial system has been increasingly brought into discussions which sought to explain complex reactions within the body economy. Every branch of medicine and almost every abstruse subject in it have been coupled with this system. To the dermatologist, no less than to any other investigator, the reticuloendothelial system has gained in importance at least in building several important theories. Thus there is evidence that the specific action of the arsphenamines is mediated through the reticulo-endothelial system ; likewise the great postulated function of the skin as an immunity organ is related to this system, as is also the related subject of allergy. An important part of the reticulo-endothelial system, if only because of its mere bulk, is the spleen. This organ, which was so long a mystery to biologists and which has been cast in all sorts of rôles, has been recently used therapeutically in