The Dollar Hen Part 10

These are two princ.i.p.al types of box incubators now in use. In the earliest of these, the eggs were heated by radiation from a tank of hot water. These machines depended for ventilation or, what is much more important, evaporation, upon chance air currents pa.s.sing in and out of augur holes in the ends or bottom of the machine.

The second, or more modern type, warms the eggs by a current of air which pa.s.ses around a lamp flue where, being made lighter by the expansion due to heat, the air rises, creating a draft that forces it into the egg chamber. There it is caused to spread by muslin or felt diaphragms so that no perceptible current of air strikes the eggs. This type is the most popular type of small incubator on the market. Its advantage will be more readily seen after the discussion of the principles of incubation.

Hazy tales of Egyptian incubators have gone the rounds of poultry papers these many years. More recently some accurate accounts from American travelers and European investigators have come to light, and as a result, the average poultry editor is kept busy trying to explain how such wonderful results can be obtained "in opposition to the well-known laws of incubation."

The facts about Egyptian incubators are as follows: They have a capacity of 50 to 100 thousand eggs, and are built as a single large room, partly underground and made of clay reinforced with straw. The walls are two or three feet thick. Inside, the main rooms are little clay domes with two floors.

The hatching season begins the middle of January and lasts three months. A couple of weeks before the hatching begins, the fireproof house is filled with straw which is set afire, thoroughly warming the hatchery. The ashes are then taken out and little fires built in pots are set around the outside of the big room. The little clay rooms with the double floors are now filled with eggs. That is, one is filled at a time, the idea being to have fresh eggs entering and chicks moving out in a regular order, so as not to cause radical changes in the temperature of the hatchery.

No thermometer is used, but the operator has a very highly cultivated sense of temperature, such as is possessed by a cheese maker or dynamite dryer. About the twelfth day the eggs are moved to the upper part of the little interior rooms where they are further removed from the heated floor. The eggs are turned and tested out much as in this country. They are never cooled and the room is full of the fumes and smoke of burning straw. The ventilation provided is incidental.

This is about the whole story save for results. The incubator men pay back three chicks for four eggs, and take their profits by selling the extra chicks that are hatched above the 75 per cent.

This statement is in itself so astonishing and yet convincing, that to add that the hatch runs between 85 per cent. and 90 per cent. of all eggs set, and that the incubators of the Nile Delta hatch about 75,000,000 chicks a year seems almost superfluous. As for the explanation of the results of the Egyptian incubators compared with the American kerosene lamp type, I think it can best be brought about by a consideration in detail of the scientific principles of incubators.

Principles of Incubation.

HEAT.--To keep animal life, once started, alive and growing, we need: First, a suitable surrounding temperature. Second, a fairly constant proportion of water in the body substance. Third, oxygen.

Fourth, food.

Now, a fertile egg is a living young animal and as such its wants should be considered. We may at once dispose of the food problem of the unhatched chick, by saying that the food is the contents of the egg at the time of laying, and as far as incubation is concerned, is beyond our control.

In consideration of external temperature in its relation to life, we should note: (A) the optimum temperature; (B) the range of temperature consistent with general good health; (C) the range at which death occurs. Just to show the principle at stake, and without looking up authorities, I will state these temperatures for a number of animals. Of course you can dispute the accuracy of these figures, but they will serve to ill.u.s.trate our purpose:

External External External Internal Internal Optimum Healthful Fatal Optimum Fatal Point Range Range Point Range

Man 70 0 to 100 50 to 140 98 90 to 106

Dog 60 70 to 140 70 to 140 101 95 to 110

Monkey 90 30 to 140 30 to 140 101 95 to 108

Horse 80 20 to 120 20 to 120 99 95 to 105

Fowl 80 20 to 140 20 to 140 107 100 to 115

Newly hatched chick 90 70 to 100 40 to 120 108 100 to 115

Fertile egg at start of incubation 103 32 to 110 31 to 125 103 31 to 125

Egg incubated three days 103 98 to 105 80 to 118 103 95 to 118

Egg incubated eighteen days 103 75 to 105 50 to 118 106 98 to 116

This table shows, among other things, that we are considering in the chick not a new proposition to which the laws of general animal life do not apply, but merely a young animal during the process of growth to a point where its internal mechanism for heat control, has power to maintain the body temperature through a greater range of external temperature change.

In the cooling process that occurs after laying the living cells of the egg become dormant, and like a hibernating animal, the actual internal temperature can be subjected to a much greater range than when the animal is active. After incubation begins and cell activity returns, and especially after blood forms and circulation commences, the temperature of the chick becomes subject to about the same internal range as with other warm blooded animals.

In the case of fully formed animals, the internal temperature is regulated by a double process. If the external temperature be lowered, more food substance is combined with oxygen to keep up the warmth of the body, while, if the external temperature be raised, the body temperature is kept low by the cooling effects of evaporation. This occurs in mammals chiefly by sweating. Birds do not sweat, but the same effect is brought about by increased breathing. Now, the chick gradually develops the heat producing function during incubation, until towards the close of the period it can take care of itself fairly well in case of lowered external temperature. The power to cool the body by breathing is not, however, granted to the unhatched chick, and for this reason the incubating egg cannot stand excess of heat as well as lack of it.

The practical points to be remembered from the above are:

First: Before incubation begins, eggs may be subjected to any temperature that will not physically or chemically injure the substance.

Second: During the first few days of the hatch, eggs have no appreciable power of heat formation and the external temperature for any considerable period of time can safely vary only within the range of temperature at which the physiological process may be carried on.

Third: As the chick develops it needs less careful guarding against cooling, and must still be guarded against over-heating.

Fourth: It should be remembered, however, that eggs are very poor conductors of heat, and if the temperature change is not great several hours of exposure are required to bring the egg to the new temperature.

Temperature is the most readily observed feature about natural incubation and its control was consequently the first and chief effort of the early incubator inventors.

A great deal of experimental work has been done to determine the degree of temperature for eggs during incubation. The temperature of the hen's blood is about 105 to 107 degrees F. The eggs are not warmed quite to this temperature, the amount by which they fail to reach the temperature of the hen's body depending, of course, upon the surrounding temperature. 103 degrees F. is the temperature that has been generally agreed upon by incubator manufacturers. Some of these advise running 102 degrees the first week, 103 degrees the second, 104 degrees the third. As a matter of fact it is very difficult to determine the actual temperature of the egg in the box incubator. This is because the source of heat is above the eggs and the air temperature changes rapidly as the thermometer is raised or lowered through the egg chamber. The advice to place the bulb of the thermometer against the live egg is very good, but in practice quite variable results will be found on different eggs and different parts of the machine.

With incubators of the same make, and in all appearances identical, quite marked variation in hatching capacity has been observed in individual machines. Careful experimentation will usually show this to be a matter of the way the thermometer is hung in relation to the heating surfaces and to the eggs. Ovi-thermometers, which consists of a thermometer enclosed in the celluloid imitation of an egg, are now in the market and are perhaps as safe as anything that can be used.

As was indicated in the previous section greater care in temperature of the egg is necessary in the first half of the hatch. The temperature of 102 degrees F. as above given is, in the writer's opinion, too low for this portion of the hatch. An actual temperature of 104 degrees at the top of the eggs will, as has been shown by careful experimental work, give better hatches than the lower temperature.

Moisture and Evaporation.

The subject of the water content of the egg and its relation to life, is the least understood of poultry problems.

The whole study of the water content of the egg during incubation hangs on the amount of evaporation. Now, the rates of evaporation from any moist object is determined by two factors: vapor pressure and the rate of movement of the air past the object. As incubation is always carried on at the same temperature, the evaporating power of the air is directly proportioned to the difference in the vapor pressure of water at that temperature, and the vapor pressure of the air as it enters the machine. Thus, in order to know the evaporative power of the air, we have only to determine the vapor pressure of the air and to remember that the rate of evaporation is in proportion to this pressure, i.e.: when the vapor pressure is high the evaporation will be slow and the eggs remain too wet, and when the vapor pressure is low the eggs will be excessively dried out.

The reader is probably more familiar with the term relative humidity than the term vapor pressure, but as the actual significance of relative humidity is changed at every change in outside temperature, the use of this term for expressing the evaporating power of the air has led to no end of confusion.

The influence of air currents on evaporation is to increase it directly proportional with the rate of air movement. Thus, 10 cubic feet of air per hour pa.s.sing through an egg chamber would remove twice as much moisture as would 5 cubic feet.

If the percentage of water in any living body be changed a relatively small amount, serious disturbances of the physiological processes and ultimately death will result. The mature animal can, by drinking, take considerable excess of water without danger, for the surplus will be speedily removed by perspiration and by the secretion from the kidneys. But the percentage of water in the actual tissues of the body can vary only within a narrow range of not more than three or four per cent. The chick in the sh.e.l.l is not provided with means of increasing its water content by drinking or diminishing it by excretion, but the fresh egg is provided with more moisture than the hatched chick will require, and the surplus is gradually lost by evaporation. This places the water content of the chick's body at the mercies of the evaporating power of the air that surrounds the egg during incubation.

To a.s.sume that these risks of uncertain rates of evaporation is desirable, is as absurd as to a.s.sume that the risks of rainfall are desirable for plant life. As the plants of a certain climate have become adapted to the amount of soil moisture which the climate is likely to provide, so the egg has by natural selection been formed with about as much excess of water as will be lost in an average season under the natural conditions of incubation. Plant life suffers in drought or flood, and likewise bird life suffers in seasons of abnormal evaporative conditions. This view is substantiated by the fact that the eggs of water fowl which are in nature incubated in damper places, have a lower water content than the eggs of land birds.

The per cent. of water contained in the contents of fresh eggs is about 74 per cent., or about 65.5 per cent, based on the weight, sh.e.l.l included. Unfortunately no investigations have been made concerning the per cent. of water present in the newly hatched chick.

Upon the subject of the loss of water for the whole period of incubation, valuable data has been collected at the Utah, Oregon and Ontario Experiment Stations.

In these tests we find that as a rule the evaporation of eggs under hens is less than in incubators. With both hens and incubators, the rate of evaporation is greatest at the Utah Station, which one would naturally expect from the climate. The eggs under hens at the Ontario Station averaged about 12 per cent. loss in weight, and those at the Utah Station about 15 per cent. At both stations, incubators without moisture ran several per cent. higher evaporation than eggs under hens. The conclusions at all stations were that the addition of moisture to incubators was a material aid to good hatches of livable chicks.

At Ontario the average evaporation ran from as low as 7 per cent. At Utah it reached as high as 24 per cent. Now as the entire loss of weight is loss of water, the solid contents remaining the same, and as the original per cent, of water contained in the egg (sh.e.l.l included) is only 65.5, the chicks of the two lots with the same amount of solid substance would contain water in the proportion of 58.5 to 41.5. Based on the weight of the chick, this would make a difference of water content of over 25 per cent.

That human beings or other animals could not exist with such differences in the chemical composition of the body, is at once apparent. In fact I do not believe that the chick can live under such remarkable circ.u.mstances. As I have picked the extreme cases in the series given, it is possible that these extremes were experimental errors, and as in the Utah data, no information is given as what happened to the chicks, I have no proof that they did live. But from the large number of hatches that were recorded below 9 per cent, and above 15 per cent., giving a variation of the actual water content in the chick's body of about 10 per cent., it is evident that chicks do hatch under remarkable physiological difficulties. One explanation that suggests itself is, that as there is considerable variation in evaporation of individual eggs due to the amount of sh.e.l.l porosity, and the chicks that hatch in either case may be the ones whose individual variations threw them nearer the normal.

By a further study from the Ontario data of the relation of the evaporation to the results in livable chicks, it can be readily observed that all good hatches have evaporation centering around the 12 per cent. moisture loss, and that all lots with evaporations above 15 per cent. hatch out extremely poor.

The general averages of the machines supplied with some form of moisture was 35 per cent. of all eggs set, in chicks alive at four weeks of age, while the machines ran dry gave only 20 per cent. of live chicks at a similar period.

Now, I wish to call attention to a further point in connection with evaporation. If the final measure of the loss of weight by evaporation were the only criterion of correct conditions of moisture in the chick's body, the hatches that show 12 per cent., or whatever the correct amount of evaporation may be, should be decidedly superior to those on either side. That they are better, has already been shown. But they are far from what they should be.