It is well known that the ectoparasitic Arthropods often produce in their host various skin reactions such as macules, wheals and haemorrhages, which in many cases are due to the salivary secretion of these ectoparasites. Nuttall and Strickland (1908) were the first to find an anticoagulin (called “Ixodin” by Sabbatani) in the salivary glands and alimentary canal of Argas persicus. Bruck (1919) found that the organs of Culex contained a haemolytic- and urticaria-producing substance called by him “Culicin.” His study was not, however, precise, because he ground up the entire bodies of the gnats, thereby mixing up secretions, excretions and fragments of organs, some of which would never enter a wound in the process of blood sucking. Moreover, the urticaria following mosquito bite was found by Schaudinn to be due to the yeast present in the oesophageal diverticula of mosquito. Klausner (1916) states that the secretions of the salivary glands in Cimex are soluble in water and alcohol, are haemolytic and produce urticaria; he found also that they do not contain formic acid and that immunity to their effects is not acquired. Nuttall (1918) dealing with the effects of salivary glands of Phthirus on human skin states that the bluish spots of the skin are especially marked after biting of adult lice, that they have nothing to do with the blue spots in the fat body of the lice and that they are probably derived from the exuded and altered blood of man.