the service mask with an oxygen-breathing apparatus and provide a two-way valve so that either the service canister or oxygen may be used as the situation requires (see Fig. 120).

The Horse Mask

The horse mask (Fig. 121) is a device to protect the respiratory tract

Fic. 121.—Amor Iran horac mask in position (World War type).

of a horse or mule from lung injurants. It is a bag made of layers of cheese cloth treated with chemical which neutralize the gas when air is breathed through if.

As horses and mules never breathe through the mouth and as their eyes are not seriously affected by lacrimators, the mask covers the nostrils and upper jaw of the animal only.

The mask is provided with a canvas or leather pad which fits into the animal's mouth preventing him from biting through the mask; a drawstring to insure tight fit of the bag over the npjwr jaw; a simple head harness which fits over the head and ears and is retained in place by a throat latch. When not in use, the mask is carriis.l in a waterproof burlap bag, which hangs under ihe lower jaw, attached to the halter.

To adjust the mask slip the mouthpiece pad well into the mouth, the • ijH n end of the bag covering the nostrils; adjust the head harness over the head; fasten the throat latch. The drawstring should be tightened so that the edge of the bag fits tightly over the upper jaw several inches above the nostrils.

Horse masks are primarily for protection of draft animals required for work through gas-contaminated areas. The mask greatly impedes tInflow of air to the horse's lungs. As horses doing heavy work or running require a large volume of air, they should be given frequent rests white at work wearing masks and should not be required to run.

The Dog Mask

The dog mask is somewhat similar to the horse mask, except that it «•overs both jaws as well as the nostrils, since a «log breathes through lx>th nose and mouth. As dogs are not used in the American Arm}', dog masks are not authorized.

The Pigeon Mask

Impregnated flannelette bags are provided for gas protection of pigeons used in war. The dimensions of the bag are 15 by 15 by 24 in. and it is designed to fit over the pigeon cage, the open end being drawn together tightly at the top by means of a drawstring. When for any reason pigeons cannot be protected they should be released at once.

Use ok the Gas Mask

Gas masks are now made in but one (universal) size which has been s|>eciallv designed to fit any type of face. The faccpiece is made big enough to fit the largest face, on the principle of a flexible conical cap. It can l>e adjusted to fit smaller faces by entering the face further into the mask. The universal faeepiece has been extensively tested and has been found to fit all sizes and types of faces to date. If subsequent experience should show that certain unusually variant types of faces, especially very small-sized faces, cannot be fitted with the universal facepicce, an additional small-size mask will also be supplied for such cases.

The World War type of mask with its uncomfortable nose clip and mouthpiece had a double line of protection. Proper fit of the facepicce was hence not vital as it i< with the present mask. As the integrity of the present mask depends uj>oii projier fitting, its ini|>ortanee cannot lie too strongly emphasized.

There are two tests for testing the Jit of a mask.

The miction text gives a good indication of the fit of the mask and should invariably be applied during the fitting procedure. It consists of three steps as follows:

1. Adjust the mask to the face.

2. Exhale fully.

3. Pinch the corrugated tube tightly and inhale.

The facepicce should now collapse tending to cling to the face and the w-arer should be unable to breathe. If the vacuum thus formed inside

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