(2) The systemic effects due to the absorption of the substance into the blood stream, and its distribution to the various tissues of the body. The most striking observation about the symptoms of mustard gas poisoning is the latent period which elapses after exposure before any serious objective or subjective effects are noted. The developments of the effects are then quite slow, unless very high superlethal doses have been inhaled. At first it was a very serious question whether or not the temporary blindness resulting from mustard gas would not be permanent. Later, as the depth and seriousness of some of the body burns became well known, it was a seven-day wonder that no permanent blindness occurred. The reason seems to be largely a mechanical one. The constant winking of the eyelids apparently washes the mustard gas off the eyeball and carries it away so that not enough remains to burn to the depth necessary to cause permanent blindness. Due to the very slight concentrations ordinarily encountered in the field, resulting from a very slow rate of evaporation, the death rate is very low, probably under 1 per cent among the Americans gassed with mustard during the war. If, on the other hand, the gas be widely and very finely dispersed by a heavy charge of explosive in the shell, the gas is very deadly. In such cases the injured breathe in minute particles of the liquid and thus get hundreds of times the amount of gas that would be inhaled as vapor. This so-called “high explosive mustard gas shell” was a German development in the very last months of the war. Its effects were great enough to make it certain that in the future large numbers of these shell will be used. The similarity of the symptoms and pathological effects after the inhalation of large amounts of the vapor and those following an injection of an olive oil or water solution of mustard gas led Marshall and his associates to conclude that in high concentrations mustard gas is absorbed through the lungs. A further bit of evidence consists in the isolation of the hydrolysis product, dihydroxyethylsulfide, in the urine of animals poisoned by inhalation of mustard gas. This product is not toxic and is not responsible for the effects of mustard gas. Hydrochloric acid, however, does produce very definite effects upon the animal and may cause death. From these facts Marshall[21] has proposed the following mechanism of the action of mustard gas: [Footnote 21: Marshall, Lynch and Smith, _J. Pharmacal_, =12=, 291-301 (1918).]