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 shell. Evidently the hen was sacrificing her own health by breathing impure air in order to soften up the shells 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 quantities involved, has no perceptible effect upon egg shells, 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 accumulated, of course, fails to prove the theory, but it is interesting as further evidence of the needlessness in the old fear of insufficient ventilation.