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largely from the feet. Among the most important are sheep's foot oil, horse foot oil, and neat's foot oil, which is obtained from the feet of cattle. These oils are all highly valued for technical purposes, especially for lubricating, and for this purpose bring a very high price. They are not used or should not be used for edible purposes, though they perhaps may sometimes be used in cooking. Neat's foot oil, especially, on account of its high price, is often subjected to adulteration, and is mixed for this purpose with cheap vegetable oils, such as cottonseed. Fish oil is also often used in the adulteration of neat's foot oil, though the addition of any of these oils to neat's foot oil raises the iodin number to a very high degree, and hence this addition is easily detected by the chemist.
Lard Oil.-Lard oil is one of the most important of terrestrial animal oils. It is made from lard by melting it and allowing it to slowly cool. The stearin in the product crystallizes first, and when it reaches a condition favoring the separation of the stearin the mass is subjected to straining or pressure, whereby the olein or liquid portion of the oil is separated, and thus, having been freed from the most of its stearin, remains liquid at ordinary temperature. The residue is known as lard stearin and is largely employed in the preparation of lard to give it a higher melting point and in the manufacture of oleomargarine.
Lard oil is used to some extent for edible purposes and is itself sometimes employed in the manufacture of oleomargarine when mixed with tallow or tallow stearin.
Properties of Lard Oil.—It is evident that the chemical and physical properties of lard oil are determined by the completeness with which the stearin is separated. Inasmuch, however, as the conditions of manufacture are nearly constant, lard oil has characteristics of a physical and chemical nature which do not vary greatly. The specific gravity of lard oil at 15 degrees. is about .916, and its iodin number varies from 68 to 75. When made of the best material it has a neutral taste, not an unpleasant odor, and, therefore, can be used for edible purposes without introducing any characteristic odor or flavor into the prepared food. In point of fact, however, it is not used to any extent for edible purposes except in the manufactured articles above mentioned. When carefully made and of the proper quality pure lard oil should be practically free from free acid.
Adulterations. On account of the high value of lard oil for lubricating and other purposes it has been subjected to extensive adulterations. The addition of cheaper animal oils or vegetable oils has been largely practiced. Fish oil, blubber oil, and other marine animal oils have also been freely used in the adulteration of lard oil whenever the difference in price has rendered it advisable. These adulterations are of such a character that they can be detected only by the skilled microscopist and chemist. The other animal oils, both of marine and terrestrial origin, while important from a technical point of view, are of no significance in respect of edible qualities.
POULTRY AND GAME BIRDS.
Application of Name.-The term poultry for descriptive purposes may be applied to those classes of feathered domesticated birds used for human food. It, therefore, includes practically all of the domesticated fowls. The term game bird, for the purpose of this manual, is applied to feathered animals which are wild and which are used for human food. This also may apply to almost all wild birds, since at times they practically all have been used for food purposes. Here only those in common use, both domesticated and wild, will be referred to. In connection with poultry the eggs of the birds will be considered.
The principal domesticated fowls which are used for human food are chickens, turkeys, geese, ducks, and guinea hens. The most common of all is the chicken, the next perhaps are turkeys in this country and the goose in Europe. The others are more infrequently used but are highly prized.
Chicken. The chicken scientifically is known as Gallus domesticus. For food purposes the chicken is eaten at various ages. The very young chicken is commonly called a broiler and is prepared for the table at varying ages from six to twelve weeks. Young chickens are also very commonly called spring chickens, since they occur in greater abundance in the spring than at any other time. Since the introduction of the modern method of incubation, however, the spring chicken may be had at all seasons of the year. The "broiler" and "spring chicken" may be regarded as synonymous terms, though the larger chicks are usually called spring chickens instead of broilers.
Full Grown Chickens.-The full grown chicken is better suited for food when still young. The flesh loses flavor and gains in toughness as the chicken grows older. There is no legal limit fixing the division of chickens into different classes with respect to age and the only criterion is the price and taste of the consumer. There is, perhaps, no objection to the use of old chickens for food purposes, provided they are not sold fraudulently as young chicks. The size and toughness of the pieces one often secures when ordering spring chicken is an indication that the age limit is not very definitely established. Both hens
and roosters are used for food purposes, but especially the young roosters are devoted to food purposes while the young hens are often kept for the production of eggs.
Preparation of Chickens for Food Purposes.-In former times, when the chickens of commerce were derived chiefly from the farm, no special preparation was made before the chicken was marketed. The eggs were hatched in the old-fashioned way by the hens and the chicks sold to hucksters or in market, at various ages and without any special preparation or control. All this has been changed in later times by the introduction of scientific methods of breeding poultry. It has been demonstrated that the breeding and care of poultry
require as much scientific and economic attention as is devoted to any other successful business.
The Incubator.-The introduction of the incubator for the hatching of eggs with the other necessary arrangements for the caring for young chicks has perhaps done more than any other one thing to revolutionize the method of preparing poultry for the market. By the use of the incubator the hatching of chicks is regulated with the utmost degree of nicety. A larger percentage of eggs produce chicks and the expense of the incubating process is greatly diminished. The incubator is in its widest significance a thermostat in which the eggs may be placed and maintained constantly at the temperature of the hen's body, namely, about 102 degrees F. The arrangement of the chicken house and the other environments of the young chick are shown in Fig. 12.
CARE OF YOUNG CHICKS.
Care of Young Chicks.-The principal points in the care of young chicks are fresh air, freedom from infection by epidemic or contagious diseases, exclusion of insect pests, even high temperature, and abundance of food. The young chick is especially sensitive to low temperatures and must be protected from cold, especially from cold rains. For this reason the chicks, after hatching, must be kept, if it is not summer time, in a room where the temperature can be regulated until they have acquired some degree of strength and vitality. The temperature of the chicken house for the young birds should not be lower than 85 or 90 degrees F.
A temperature of about 102 degrees F. is found very favorable to the development of the chicks in the eggs, although the temperature may sometimes fall to 101 or rise to 103 degrees F. without materially affecting the results. Experiments show that too low a temperature arrests the development of the chick. On the contrary there seems to be no indication that an increase of heat, up to 103 degrees F., has any tendency to kill the chick in the last stages of development. It is found best in all cases to set the eggs in the incubator as soon after they are laid as possible. Where the age of the egg is not known it should be carefully candled, that is, held up between the eye and a light in order to determine its condition. In old eggs, the yolk, on-candling, becomes more or less diffused with the' white and such eggs are to be rejected for incubator purposes as they are not likely to produce chickens. The fertility of the egg must also be assured before placing in the incubator. An unfertilized egg is so much loss in the incubator since it might have been used for food purposes, since the egg, for marketable purposes, when fresh is just as good as a fertilized egg. It is an observed fact that the complete fertilization of the egg, that is, the proper union of the male and female germ cells, is not always complete at the time the egg is laid, but the mingling of the two elements takes place under proper conditions afterwards. The development will also depend upon the vitality of the germ and its component parts. Just, for instance, as the color of the feathers, the size of the body and the general character of the chick may be inherited from either parent, so the vital qualities are much more strongly shown in some eggs than in others. The proper germination of the egg may also be improved by many of the conditions of environment. In the case of eggs, any slight change which would interfere with the functions of the yolk or albumin, both of which are extremely sensitive to change, would interfere with the growth. of the embryo either by depriving it of food or subjecting it to other conditions. in which its vitality would be diminished or destroyed. The fertilized egg may be separated from the non-fertilized also by candling. At the Rhode Island station it is found that a very good light for candling is the ordinary calcium carbide bicycle lamp, placed in a proper candling box. This is a strong white light quite equal in power to the electric incandescent light and is not so trying
to the eyes.
When eggs which have been submitted to incubation permit light to shine through and show the yolk suspended in the upper half of the center as a clearly defined mass, which quickly reassumes its position in turning the egg with its long axis nearly horizontal, they are probably infertile or sterile. When, on the contrary, the yolk assumes indefinite outlines, approaching near the upper portion of the shell at the large end or appears with a thick spur upon its upper side, it may be regarded as having started to incubate. In the later stages the embryo can be plainly seen, because it becomes opaque and cuts off more of the light. In the incubation of eggs the candling is resorted to during the first few days of the experiment in order that the unfertilized eggs may be separated. The best time for the candling, if it is practiced only once, is on the sixth or seventh day of incubation. By that time all the eggs which are fertilized will be so changed as to be easily recognized by the candling process. Experience has shown that eggs which are more than two weeks old are not profitable for use in incubators since the percentage that does not hatch is so large. The incubating part of the plant is sometimes placed in the cellar over which the brooding house is built.
The brooding of young chicks is of the utmost significance. In Europe the changes in temperature are much less violent than in this country. The principal brooding houses in the United States are in the North where the temperature often falls in winter to below zero while in the summer it may rise to blood heat, a difference of over 100 degrees F. For this reason the incubating houses in the United States are often placed in cellars where the uniform conditions of temperature are more easily secured. There is no objection to this location provided proper care be taken to secure ventilation and the proper content of moisture in the atmosphere. In Great Britain the incubating houses are usually placed above ground instead of in cellars. The mean range of temperature in an incubating room in Great Britain, from March 12, 1903, to March 30, 1904, was 10 degrees. The highest temperature registered was 70 degrees on the 24th of June and the lowest 42 degrees in January. The humidity of the air was also quite constant, the lowest degree of humidity being 59 and the highest These data show a very even temperature in the room itself. Of course the temperature in the incubator is necessarily greater, being that already referred to, namely 102 degrees.
Early Market. One principal object in the raising of chicks is to force them to an early maturity in so far as size and palatability are concerned. The sooner the young broilers can be made ready for the market the more economy there is in their production. To this end they ought to receive a more abundant and specially prepared kind of food than if they were intended for ordinary farm purposes. In other words, the forcing process should be pushed as far as possible without interfering with the health and normal functions of the bird. Foods which are nutritious and stimulating and promote vigorous