The first type of American horse mask was modelled after the British and was impregnated with the Komplexene mixture (hexamethylenetetramine, glycerine, nickel sulfate mixture). This mask had too high a resistance and caused complete exhaustion in running horses. The second mask was made of a large number of layers of very open cheesecloth. It consists of two bags, impregnated with different mixtures (Komplexene and Simplexene). Horses can run two miles with this mask without showing evidences of exhaustion. Dewey gives the following method of manufacture: The chemical employed consisted of a mixture of hexamethylenetetramine (to give protection against phosgene), nickel sulfate (to protect against the possible use of hydrocyanic acid), sodium carbonate and glycerine. This solution was mixed in a heavy steam jacketed mixing kettle with heavy geared stirrers. The mixture was conducted by pipes to the impregnating apparatus which consisted of a rotary laundry washing machine. The masks were treated in this machine for 15 minutes, and then placed in a power operated wringer and the solution driven off to a given weight. Following this operation, they were suspended on wire supports and conducted through a hot air drying machine and dried to a definite weight. 378,000 horse masks were produced at the rate of 5,000 per day. [Illustration: FIG. 83.—Horse Mask—American Type.] Theoretically, horse masks and horse boots are very valuable,—practically, they did very little actual good in the field, not that they would not protect or that animals would not wear them. The trouble was with the riders and drivers. Gas attacks, coming usually at night, made adjustment of horse masks difficult at best, while in the confusion of bursting shell and smoke, the drivers absolutely forgot the horse masks or after putting on their own masks feared to try putting masks on the animals. This last was natural as most animals fight the adjustment of the mask and in so doing there is great risk that the man’s mask may be torn off and the man gassed. In the future, such masks will have even more importance than in the past, for the present methods of manufacture of mustard gas coupled with its all-round effectiveness will cause a use of it ten-fold greater than at any time in the World War. In such cases, operations will necessarily be frequently carried on over large areas thoroughly poisoned with mustard gas. Here the animals will be masked and booted before entering the gassed area, and remain so until they leave it. In the torn and broken ground around the front line there will always be need for animal transportation,—wagon, cart and horse—as in such places it is far better in nearly all cases than motor transport.