A peculiar natural defect is found in many South American goat skins, especially the Brazilian, which are often badly scratched by the animals rubbing themselves against cactus plants. Although, perhaps, more of an artificial than a natural defect, the scratches caused by cattle rubbing their hides against barbed wire constitute a serious, but easily avoidable, loss. Such a barbarous system of fencing ought never to be used. [Illustration: A KIP CONTAINING 584 HOLES CAUSED BY THE WARBLE FLY (The skin belongs to W. D. Mark & Sons, Hide Factors, Newcastle.)] [Illustration: FIG. 3 HOLE IN COW HIDE, MADE BY THE GRUB OF THE WARBLE FLY (Magnified fifteen times)] The most serious loss in connection with hides and skins, however, is caused by the warble flies, _hypoderma bovis_ and _hypoderma lineatum_, which lay their eggs on the hides of cattle. It has been a debatable point for some years as to whether these eggs hatched and burrowed their way into the hides from the exterior or were licked and swallowed by the cattle and, after traversing the digestive tract, pierced the hide from the interior. Professor Carpenter, who has been experimenting a number of years for the Department of Agriculture for Ireland, has succeeded in taking a remarkable photograph (Fig. 3) which proves that the larvae penetrate the hide from the exterior. These develop within the hide and often penetrate to the flesh before they fall out to the ground and change into the fly. The most effective way of getting rid of the pest is to destroy the larvae, either by cutting them out and crushing them under foot, or by piercing them with a hot needle. No satisfactory dressing has yet been found, but Prof. Carpenter states that sulphur dioxide is effectual, if a good method of applying it can be devised. While sheep skins are immune from the attacks of the warble fly, they are often damaged by the blow-fly, lice, keds, and ticks; by scab caused by the action of a mite or acarus; and by "cockle," which causes a wrinkled grain. The origin of cockle is not definitely known, but it is a seasonal defect which begins to show on a large number of skins in December and does not disappear until the sheep are shorn in the following spring. CHAPTER III TANNING MATERIALS Tanning materials are derived from the vegetable, mineral, and animal kingdoms. The vegetable materials used are woods, barks, shrubs, leaves, and fruits, either in their natural state or in the form of extracts. The majority of the minerals have a more or less tanning effect on animal fibres, but the principal are basic chrome salts, formaldehyde, alum and salt. Titanium, iron, cerium and potassium salts also convert skins into leather, but are not yet used commercially. The animal matters that will convert skins into leather consist of oxidised oils (chamois leather), fats, and brains (crown, Helvetia, or Preller's leather).