subject. What is the cause of this emotional or almost hysterical background from which a clear definition of the matter is only now beginning to emerge? Circumstances are to blame; the first open act of chemical warfare decided the matter.

This event, the first German cloud gas attack at Ypres, arriving at the peak of allied indignation against a series of German abuses, in particular with regard to the treatment of prisoners, left the world aghast at the new atrocity. Further, its use against entirely unprotected troops was particularly revolting. The fact that such a cloud of chlorine would have passed the 1918 armies untouched behind their modern respirators, could not be known to, nor appreciated by the relatives of the 1915 casualties. But the emotion and indignation called forth by the first use of gas has survived a period of years, at the end of which the technical facts would no longer, of themselves, justify such feeling. We would hesitate to do anything which might dispel this emotional momentum were we not convinced that, unaccompanied by knowledge, it becomes a very grave danger. If we felt that the announcement of an edict was sufficient to suppress chemical warfare we would gladly stimulate any public emotion to create such an edict. But therein lies the danger. Owing to certain technical peculiarities, which can be clearly revealed by examination of the facts, it is impossible to suppress chemical warfare in this way. As well try to suppress disease by forbidding its recurrence. But we can take precaution against disease, and the following examination will show clearly that we can take similar precautions against the otherwise permanent menace of chemical war. Further, backed by such precautions, a powerful international edict has value.

It is, therefore, our intention to present a reasoned account of the development of poison gas, or chemical warfare, during the recent war. But to leave the matter there would be misleading and culpable, for, however interesting the simple facts of the chemical campaign, they owed their being to a combination of forces, whose nature and significance for the future are infinitely more important. The chief cause of the chemical war was an unsound and dangerous world distribution of industrial organic chemical forces. Unless some readjustment occurs, this will remain the "point faible" in world disarmament. We, therefore, propose to examine the relationships between chemical industry, war, and disarmament.

Some Preliminary Explanation.—The chemistry of war, developed under the stress of the poison gas campaign, is of absorbing chemical and technical interest, but it has none the less a general appeal. When its apparently disconnected and formidable facts are revealed as an essential part of a tense struggle in which move and counter-move followed swiftly one upon the other, its appeal becomes much wider. Therefore, in order not to confuse the main issue in the following chapters by entering upon tiresome definitions, it is proposed to conclude the present chapter by explaining, simply, a number of chemical warfare conceptions with which the expert is probably well acquainted.

"Poison Gas" a Misleading Term—Poison gas is a misleading term, and. our subject is much better described as "chemical, warfare." Let us substantiate this by examining briefly the types of chemicals which were used. In the first place they were not all gases; the tendency during the war was towards the use of liquids and solids. Even the chemicals which appeared as gases on the field of battle were transported and projected as liquids, produced by compression. As the poison war developed, a large number of different chemicals became available for use by the opposing armies. These can he classified, either according to their tactical use, or according to their physiological effects on man.

The British, French, American, and German armies all tended to the final adoption of a tactical classification, but the French emphasised the physiological side. Let us use their classification as a basis for a review of the chief chemicals concerned.

The French Physiological Classification;—Asphyxiating Substances;— Toxic Substances;—Chemicals or poison gases were either asphyxiating, toxic, lachrymatory, vesicant, or sternutatory. It is perfectly true that the asphyxiating and toxic substances, used during the war, produced a higher percentage of deaths than the other three classes, but the latter were responsible for many more casualties. The so-called asphyxiating gases produced their effect by producing lesions and congestion in the pulmonary system, causing death by suffocation. The best known substances of this type was chlorine, employed in the liquid state in cylinders on the occasion of the first German gas attack, but the most formidable were phosgene (an important substance required in the manufacture of dyes), diphosgene, chlor-picrin, made from bleaching powder and picric acid, brom-acetone, which was also a powerful lachrymator, and diphenylchlorarsine, known as sneezing gas, the first sternutatory or sneezing compound to appear on the front in large quantities. The toxic compounds were so called because of their specific effect upon particular parts of the organism such as, for example, the nervous system. The chief example, with regard to the military value of which there has been much dispute, was prussic, or hydrocyanic, acid. The French had definite evidence of the mortal effect of this compound upon German gunners, but it was doubted by other Allies whether French gas shell produced a sufficient concentration of gas to be of military value. It was a kill or cure compound, for recovery was rapid from any concentration which did not produce death.

A prominent Cambridge physiologist, in the heat of the controversy on this matter, made a very brave and self-sacrificing experiment. He entered a chamber of prussic acid which was sufficiently concentrated to cause the death of other animals which were present. They were removed in time, and he escaped because the concentration was not a mortal one for man. This was, in a sense, an experimentum crucis and, although it did not disprove the extreme danger of prussic acid, if employed in high concentrations, it showed, on the other hand, that it was difficult to gauge the military value by field experiments; battle results were necessary. The Germans' disappointment with the use of arsenic compounds confirms this need for battle evidence.

Lachrymators.—There is hardly need to dwell on the next class, the lachrymator. These compounds were employed on a large scale to produce temporary blindness by lachrymation, or weeping. We give later some interesting examples of their use on the front. It is an arresting thought that even as early as 1887 Professor Baeyer, the renowned organic chemist of Munich, in his lectures to advanced students, included a reference to the military value of these compounds.

Vesicant or Blistering Compounds.—It was the introduction of the fourth, the vesicant class, which revealed, more than any other enemy move, the great possibilities inherent in chemical warfare. These compounds, the chief of which was mustard gas, produced vesicant, or skin burning, effects, which, although rarely mortal, were sufficient to put a man out of action for a number of months. Mustard gas resulted from pure scientific investigation as early as 1860. Victor Meyer, the famous German chemist, described the substance in 1884, indicating its skin-blistering effects. There is evidence of further investigation in German laboratories a year before the outbreak of war, and whatever the motive for this work, we know that mustard gas must have received the early attention of the German War Office, for it was approved and in production early in 1917. Although the Medecin aide-major Chevalier of the French services drew attention to its importance in 1916, the French