The quality of our home supply of hides is very valuable, being determined by the conditions of the animal's life, its precise breed, and by other factors such as age and sex. The best hides are usually obtained from animals which have been most exposed to extremes of wind and cold, as such conditions tend naturally to develop a thicker and more compact covering. Broadly speaking, these include the hides from cattle of the northern and hilly districts. The age of the animal when killed is also a dominating factor. Calf skins are very soft, fine grained and compact, the state of rapid growth favouring the existence of much interfibrillar substance. The youngest animals supply suitable raw material for various light leathers (see Part II., Section V.), and are also very suitable for chrome work (see Part III., Section III.). Bull and cow hides, on the other hand, are from animals whose growth is complete, and show in consequence a lack of interfibrillar substance, coarse fibres and a rough and often wrinkled grain. The resulting leather tends consequently to be spongy, thin, empty and non-waterproof. Intermediate between these extremes are the hides of the ox and heifer, large, yet of good texture, and well supplied with interfibrillar substance. These hides are much the best for sole leather, a firm, smooth-grained and well-filled leather being needed. The term "kip" is often applied to small hides and to hides from large calves. In the trade, however, "kip" is sometimes used also for larger hides, as a verbal enhancement of value; just as a man with a few old fowls is said to keep "chickens." Cow hides tend to be "spready," _i.e._ to have a large area per unit weight, and are therefore more suitable for dressing leather. Bull hides are thicker in the neck and belly, and thinner in the back, which characteristics reduce their commercial value. Market hides are sold by weight, and are therefore classified chiefly by their weight, which is marked on near the tail by a system of knife-cuts. The animals are flayed after cutting the hide down the belly and on the inside of the legs.