The Dollar Hen

by Milo Hastings

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 buttermilk 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 shell so the chick could break out easier.

At the Guelph Station the conception was that the carbon dioxide might dissolve the lime of the shell for the chick to use in "makin' hisself." As an egg could not be analyzed fresh and then hatched, a number were analyzed from the same hens and others from those hens were then incubated with the various amounts of carbon dioxide, buttermilk, 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 shell 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 shell, 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."

The Box Type of Incubator In Actual Use.

Although the fact is not so advertised and frequently not recognized even by the makers, the success of existing incubators is directly proportional to the extent with which they control evaporation. In order to show this I have only to call attention briefly to two or three of the most successful types of incubators on the market.

Let me first repeat that evaporation increases with increased air currents and with decreased vapor pressure. Now, the vapor pressure undergoes all manner of changes with the passing of storm centers and the changes of prevailing winds. But there is a general tendency for vapor pressure to increase with increase in outside temperature. Now, the movement of air in all common incubators depends upon the draft principle and the greater the difference in machine temperature and outside temperature the greater will be this draft. Thus, we have two factors combining to cause variation in the rate of evaporation. The tendency for the rate of airflow to vary is diminished when a cellar is used for an incubator room, but the cellar does not materially remedy the climatic variation in vapor pressure.