The idea for a respirator in the form of a helmet to go right over the head is stated to have originated from an idea of a sergeant of the Canadians who was gassed at Ypres, who stated that he had seen some of the Germans through the gas cloud with things that looked like flour bags pulled over their heads. It was thought that something of this kind could actually be made use of, and experiments showed that it was really a practical idea, because breathing is done through a very big surface and not only through the chemicals directly in front of the mouth and nose, as in the case of the respirator. By having a big surface it is possible to have thinner material and there is, therefore, less resistance to breathing. All that is required is to tuck the helmet down inside the jacket and button the latter tightly round it at the neck, and if this is done there is little possibility of gas leaking in. As a matter of fact there is no evidence that the Germans ever did use anything of the kind. The first types of smoke helmet were made of flannel and had a window for seeing through which was made of mica or celluloid. The helmets were soaked in the same kind of solution--hypo, carbonate of soda and glycerin--that had been employed for the respirators. Helmets of this kind were capable of standing up against really considerable concentrations of chlorine, and they were quickly recognised both by the troops and by experts as being a very big improvement on the old respirator. These helmets were made and issued to the troops as quickly as possible and a few of them were actually used in the attack of May twenty-fourth. Men unpracticed in their use were apt to find them hot and stuffy, and, not realising that the feeling wears off, were often inclined to think that they were being suffocated or gassed. As a matter of fact well-drilled men could do almost anything while wearing the helmet, the chief difficulty being that of limited vision. After wearing the helmet for a short time the celluloid window got clouded over from the moisture in the breath, but this could easily be remedied by wiping it on the forehead. In many cases also the windows got cracked or broken from the rough treatment they were bound to meet in trenches, and this was a constant danger until men learned how to fold the helmet properly so as to protect the celluloid and to place a small sheet of cardboard or thin wood over the window before folding.