An explanation is not hard to find. The correct content of moisture is not the only essential to the chick's well being at the moments of hatching, but during the whole period of incubation. Under our present system of incubation, the chick is immediately subject to the changing evaporation of American weather conditions. The data for that fact, picked at random, will be of interest. The following table gives the vapor pressure at Buffalo, N. Y., for twenty consecutive days in April:

April 1..................170 2..................130 3...................95 4..................103 5..................110 6..................106 7..................154 8..................183 9..................245 10.................311 11.................342 12.................286 13.................219 14.................248 15.................217 16.................193 17.................241 18.................306 19.................261 20.................204

Supposing a hatch to be started at the beginning of the above period, by the end of the first week, with the excessive evaporation, due to a low vapor pressure, the eggs would all be several per cent. below the normal water content; the fact that the next week was warm and rainy, and the vapor pressure rose until the loss was entirely counterbalanced, would not repair the injury, even though the eggs showed at the end of incubation exactly the correct amount of shrinkage. A man might thirst in the desert for a week, then, coming to a hole of water fall in and drown, but we would hardly accept the report of a normal water content found at the post-mortem examination as evidence that his death was not connected with the moisture problem.

The change of evaporation, due to weather conditions, is, under hens, less marked than in incubators. This is because there are no drafts under the hen, and because the hen's moist body and the moist earth, if she sets on the ground, are separate sources of moisture which the changing humidity of the atmosphere does not affect. Among about forty hens set at different times at the Utah Station and the loss of moisture of which was determined at three equal periods of six days each, the greatest irregularity I found was as follows: 1st period, 5.81 per cent; 2d period, 3.86 per cent; 3d period, 6.15 per cent. Compare this with a similar incubator record at the same station in which the loss for the three periods was 5.63, 9.18 and 2.15.

I think the reader is now in position to appreciate the almost unsurmountable difficulties in the proper control of evaporation with the common small incubator in our climate. It is little wonder that one of our best incubator manufacturers, after studying the proposition for some time, threw over the whole moisture proposition, and put out a machine in which drafts of air were slowed down by felt diaphragms and the use of moisture was strictly forbidden.

The moisture problem to the small incubator operator presents itself as follows: If left to the mercies of chance and the weather, the too great or too little evaporation from his eggs will yield hatches that will prove unprofitable. In order to regulate this evaporation, he must know and be able to control both vapor pressure and the currents of air that strike the eggs. Now he does not know the amount of vapor pressure and has no way of finding it out. The so-called humidity gauges on the market are practically worthless, and even were the readings on relative humidity accurately determined, they would be wholly confusing, for their effect of the same relative humidity on the evaporation will vary widely with variations of the out-of-door temperature.

If the operator knows or guesses that the humidity is too low, he can increase it by adding water to the room, or the egg chamber, but he cannot tell when he has too much, nor can he reduce the vapor pressure of the air on rainy days when nature gives him too much water. As to air currents he is little better off--he has no way to tell accurately as to the behavior of air in the egg chamber and changes in temperature of the heater or if the outside air will throw these currents all off, since they depend upon the draft principle.

Taking it all in all, the man with the small incubator had better follow the manufacturer's directions and trust to luck.

The writer has long been of the conviction that a plan which would keep the rate of evaporation within as narrow bounds as we now keep the temperature, would not only solve the problem of artificial incubation, but improve on nature and increase not only the numbers but the vitality or livability of the chicks. With a view of studying further the relations between the conditions of atmospheric vapor pressure, and the success of artificial incubation, I have investigated climatic reports and hatching records in the various sections of the world.

The following are averages of the monthly vapor pressures at four points in which we are interested:

Buffalo, St. Louis, San Fran- Cairo Month N.Y. Mo. cisco. Egypt January 87 98 311 279 February 81 94 310 288 March 138 224 337 287 April 171 283 332 311 May 301 423 317 328 June 466 550 345 365 July 546 599 374 413 August 496 627 382 435 September 429 506 389 372 October 285 327 342 365 November 271 225 285 321 December 143 133 243 397

A study of the extent of daily variations is also of interest. As a general thing they are less extreme in localities when the seasonal variations are also less. In Cairo, however, which has a seasonal variation greater than San Francisco, the daily variations during the hatching season are much less than in California. This is due to a constant wind from sea to land, and an absolute absence of rainfall, conditions for which Egypt is noted.

Nearness to a coast does not mean uniform vapor pressure, for with wind alternating from sea to land, it means just the opposite.

As will be readily seen the months in spring which give the best hatches, occupy a medium place in the humidity scale. The fact that both hens and machines succeed best in this period, is to me very suggestive of the possibility that with an incubator absolutely controlling evaporation, much of the seasonal variation in the hatchability would disappear.

The uniform humidity of the California coast is shown in the above table. This is not inconsistent with the excellent results obtained at Petaluma.

The Egyptian hatcher in his long experience has learned just about how much airholes and smudge fire are necessary to get results. With these kept constant and the atmosphere constant, we have more nearly perfect conditions of incubation than are to be found anywhere else in the world, and I do not except the natural methods. The climatic conditions of Egypt cannot be equaled in any other climate, but as will be shown in the last section of this chapter, their effect can be duplicated readily enough by modern science and engineering.

Mr. Edward Brown, who was sent over here by the English Government to investigate our poultry industry, was greatly surprised at our poor results in artificial incubation. Compared with our acknowledged records of less than 50 per cent. hatches, he quotes the results obtained in hatching 18,000 eggs at an English experiment station as 62 per cent. I have not obtained any data of English humidity, but it is undoubtedly more uniform than the eastern United States.

Ventilation--Carbon Dioxide.

The last of the four life requisites we have to consider is that of oxygen. The chick in the sh.e.l.l, like a fish, breathes oxygen which is dissolved in a liquid. A special breathing organ is developed for the chick during its embryonic stages and floats in the white and absorbs the oxygen and gives off carbon dioxide. The amount of this breathing that occurs in the chick is at first insignificant, but increases with development. At no time, however, is it anywhere equal to that of the hatched chicks, for the physiological function to be maintained by the unhatched chicks requires little energy and little oxidation.

Upon the subject of ventilation in general, a great misunderstanding exists. Be it far from me to say anything that will cause either my readers or his chickens to sleep less in the fresh air, yet for the love of truth and for the simplification of the problem of incubation, the real facts about ventilation must be given.

In breathing, oxygen is absorbed and carbon dioxide and water vapor are given off. It is popularly held that abundance of fresh air is necessary to supply the oxygen for breathing and that carbon dioxide is a poison. Both are mistakes. The amount of oxygen normally in the air is about 20 per cent. Of carbon dioxide there is normally three hundredths of one per cent. During breathing these ga.s.ses are exchanged in about equal volume. A doubling or tripling of carbon dioxide was formerly thought to be "very dangerous." Now, if the carbon dioxide were increased 100 times, we would have only three per cent., and have seventeen per cent. of oxygen remaining. This oxygen would still be of sufficient pressure to readily pa.s.s into the blood. We might breathe a little faster to make up for the lessened oxygen pressure. In fact such a condition of the air would not be unlike the effects of higher alt.i.tudes.

Some investigations recently conducted at the U.S. Experiment Station for human nutrition, have shown the utter misconception of the old idea of ventilation. The respiratory calorimeter is an air-tight compartment in which men are confined for a week or more at a time while studies are being made concerning heat and energy yielded by food products. It being inconvenient to a.n.a.lyze such an immense volume of air as would be necessary to keep the room freshened according to conventional ventilation standards, experiments were made to see how vitiated the air could be made without causing ill effects to the subject.

This led to a remarkable series of experiments in which it was repeatedly demonstrated that a man could live and work for a week at a time without experiencing any ill effects whatever in an atmosphere of his own breath containing as high as 1.86 per cent. of carbon dioxide, or, in other words, the air had its impurity increased 62 times. This agrees with what every chemist and physiologist has long known, and that is that carbon dioxide is not poisonous, but is a harmless dilutant just as nitrogen. This does not mean that a man or animal may not die of suffocation, but that these are smothered, as they are drowned, by a real absence of oxygen, not poisoned by a fraction of 1 per cent. of carbon dioxide.

In the same series of experiments, search was made for the mysterious poisons of the breath which many who had learned of the actual harmlessness of carbon dioxide alleged to be the cause of the ill effects attributed to foul air. Without discussion, I will say that the investigators failed to find such poisons, but concluded that the sense of suffocation in an unventilated room is due not to carbon dioxide or other "poisonous" respiratory products, but is wholly due to warmth, water vapor, and the unpleasant odors given off by the body.

The subject of ventilation has always been a bone of contention in incubator discussions. With its little understood real importance, as shown in the previous section, and the greatly exaggerated popular notions of the importance of oxygen and imagined poisonous qualities of carbon dioxide, the confusion in the subject should cause little wonder.

A few years ago some one with an investigating mind decided to see if incubators were properly ventilated, and proceeded to make carbon dioxide determinations of the air under a hen and in an incubator.

The air under the hen was found to contain the most of the obnoxious gas. Now, this information was disconcerting, for the hen had always been considered the source of all incubator wisdom. Clearly the perfection of the hen or the conception of pure air must be sacrificed. Chemistry here came to the rescue, and said that carbon dioxide mixed with water, formed an acid and acid would dissolve the lime of an egg sh.e.l.l. Evidently the hen was sacrificing her own health by breathing impure air in order to soften up the sh.e.l.ls a little so the chicks could get out. Since it could have been demonstrated in a few hours in any laboratory, that carbon dioxide in the quant.i.ties involved, has no perceptible effect upon egg sh.e.l.ls, it is with some apology that I mention that quite a deal of good brains has been spent upon the subject by two experiment stations. The data acc.u.mulated, of course, fails to prove the theory, but it is interesting as further evidence of the needlessness in the old fear of insufficient ventilation.

At the Ontario Station, the average amounts of carbon dioxide under a large number of hens was .32 of one per cent., or about ten times that of fresh air, or one-sixth of that which the man breathed so happily in the respiratory calorimeter. With incubators, every conceivable scheme was tried to change the amount of carbon dioxide.

In some, sour milk was placed which, in fermenting, gives off the gas in question. Others were supplied with b.u.t.termilk, presumably to familiarize the chickens with this article so they would recognize it in the fattening rations. In other machines, lamp fumes were run in, and to still others, pure carbon dioxide was supplied. The percentage of the gas present varied in the machines from .06 to .58 of one per cent. The results, of course, vary as any run of hatches would. The detailed discussion of the hatches and their relation to the amount of carbon dioxide as given in Bulletin 160 of the Ontario Station, would be unfortunately confusing to the novice, but would make amusing reading for the old poultryman. Speaking of a comparison of two hatches, the writer, on page 53 of the bulletin says, "The increase in vitality of chicks from the combination of the carbon dioxide and moisture over moisture only, amounting, as it does, to 4.5 per cent. of the eggs set, seems directly due to the higher carbon dioxide content." I cannot refrain from suggesting that if my reader has two incubators, he might set up a Chinese prayer machine in front of one and see if he cannot in like manner demonstrate the efficacy of Heavenly supplications in the hatching of chickens.

The practical bearing of the subject of ventilation in the small incubator is almost wholly one of evaporation. The majority of such machines are probably too much ventilated. In a large and properly constructed hatchery, such as is discussed in the last section of this chapter, the entire composition of the air, as well as its movement, is entirely under control. Nothing has yet been brought to light that indicates any particular attention need be given to the composition of such air save in regard to its moisture content, but as the control of this factor renders it necessary that the air be in a closed circuit, and not open to all out-doors, it will be very easy to subject the air to further changes such as the increasing oxygen, if such can be demonstrated to be desirable.

Turning Eggs.

The subject of turning eggs is another source of rather meaningless controversy. Of course, the hen moves her eggs around and in doing so turns them. Doubtless the reader, were he setting on a pile of door k.n.o.bs as big as his head, would do the same thing. As proof that eggs need turning, we are referred to the fact that yolks stick to the sh.e.l.l if the eggs are not turned. I have candled thousands of eggs and have yet to see a yolk stuck to the sh.e.l.l unless the egg contained foreign organism or was several months old. However, I have seen hundreds of blood rings stuck to the sh.e.l.l. Whether the chick died because the blood rings stuck or whether the blood rings stuck because the chicken died I know not, but I have a strong presumption that the latter explanation is correct, for I see no reason if the live blood ring was in the habit of sticking to the sh.e.l.l, why this would not occur in a few hours as well as in a few days.

In the year 1901 I saw plenty of chicks hatched out in Kansas in egg cases, kitchen cupboards and other places where regular turning was entirely overlooked.

Mr. J.P. Collins, head of the Produce Department of Swift & Co., says that he was one time cruelly deserted in a Pullman smoker for telling the same story. The statement is true, however, in spite of Mr. Collins' unpleasant experience. Texas egg dealers frequently find hatched chickens in cases of eggs.

Upon the subject of turning eggs the writer will admit that he is doing what poultry writers as a cla.s.s do on a great many occasions, i.e.: expressing an opinion rather than giving the proven facts. In incubation practice it is highly desirable to change the position of eggs so that unevenness in temperature and evaporation will be balanced. When doing this it is easier to turn the eggs than not to turn them, and for this reason the writer has never gone to the trouble of thoroughly investigating the matter. But it has been abundantly proven that any particular pains in egg turning is a waste of time.

Cooling Eggs.

The belief in the necessity of cooling eggs undoubtedly arose from the effort to follow closely and blindly in the footsteps of the hen. With this idea in mind the fact that the hen cooled her eggs occasionally led us to discover a theory which proved such cooling to be necessary. A more reasonable theory is that the hen cools the eggs from necessity, not from choice. In some species of birds the male relieves the female while the latter goes foraging.

But there is no need to argue the question. Eggs will hatch if cooled according to custom, but that they will hatch as well or better without the cooling is abundantly proven by the results in Egyptian incubators where no cooling whatever is practiced.

Searching for the "Open Sesame" of Incubation.

The experiment station workers have, the last few years, gone a hunting for the weak spot in artificial incubation. Some reference to this work has already been made in the sections on moisture and ventilation. Before leaving the subject I want to refer to two more efforts to find this key to the mystery of incubation and in the one case at least correct an erroneous impression that has been given out.

At the Ontario Station a patent disinfectant wash called "Zenoleum"

was incidentally used to deodorize incubators. Now, for some reason, perhaps due to the belief that white diarrhoea was caused by a germ in the egg, this idea of washing with Zenoleum was conceived to be a possible solution of the incubator problem. In the numerous experiments at that station in 1907 Zenoleum applied to the machine in various ways was combined with various other incipient panaceas and at the end of the season the results of the various combinations were duly tabulated. The machine with b.u.t.termilk and Zenoleum headed the list for livable chicks.

For reasons explained in the chapter on "Experiment Station Work,"

the idea of contrasting the results of one hatch with one sort with the average results of many hatches of another sort is very poor science. Feeling that the Station men would hardly be guilty of expressing as they did in favor of such a method without better reason, I very carefully went over the results and compared all machines using Zenoleum with all machines without it. The results in favor of Zenoleum were less marked but still perceptible. I was somewhat puzzled, as I could see no rational explanation of the relation between disinfecting incubator walls and the hatchability of the chick in its germ-proof cage. Finally I hit upon the scheme of arranging the hatches by dates and the explanation became at once apparent. The hatching experiments had extended from March to July, but the Zenoleum hatches were grouped in April and early in May, when, as one would expect from weather conditions, all hatches were running good. After allowing for this error Zenoleum appeared as harmless and meaningless as would the Attar of Roses.

The second link after the missing link of incubation to which I wish to call your attention also occurred at the Ontario Station. The latter case, however, is happier in that no unwarranted conclusions were drawn and that an interesting bit of scientific knowledge was added to the world's store. The conception to be tested was an offshoot from the carbon dioxide theory. You will remember at the Utah Station the idea was that carbon dioxide was to dissolve the sh.e.l.l so the chick could break out easier.

At the Guelph Station the conception was that the carbon dioxide might dissolve the lime of the sh.e.l.l for the chick to use in "makin'

hisself." As an egg could not be a.n.a.lyzed fresh and then hatched, a number were a.n.a.lyzed from the same hens and others from those hens were then incubated with the various amounts of carbon dioxide, b.u.t.termilk, Zenoleum, and other factors. The lime content of the contents of the fresh egg averaged about .04 grams. At hatching time the lime in the chick's body averaged about .20 grams and was always several times as great as the maximum of the eggs.

Clearly calcium phosphate of the chick's bones is made by the digestion of the calcium carbonate from the sh.e.l.l and its combination with the phosphorus of the yolk. Certainly a remarkable and hitherto unexplained fact. The amount of lime required is not great enough, however, to materially weaken the sh.e.l.l, but, of course, the process is vital to the chick as bones are quite essential to his welfare, but it is an "inside affair" of which the three-tenths of one per cent of carbon dioxide incidentally present under the hen is entirely irrelevant.

A further observation made by the investigator is that the chicks which obtained the lowest amount of lime were abnormally weak. As long as we are powerless to aid the chick in digesting lime this fact, like the other, belongs in the field of pure, rather than applied science. I think that we are safe in saying that the weakness caused the shortage of lime rather than vice versa; if the writer remembers runts in other animals are usually a little short of bone material.

The chemist of the station is to be given special credit for not jumping at conclusions. In the summary of this work he states: "There is apparently no connection between the amount of lime absorbed by the chick and the amount of carbon dioxide present during incubation."