This has given us a great deal of trouble, and those familiar with the difficulties attending the natural ventilation of houses will appreciate the obstacles met here. The change in the room temperature, the extremes of outside temperature, the faulty construction of houses, the opening and closing of doors, the dry days, the wet, muggy days, the high and low barometric pressure, but especially the direction of the wind and its strength have prepared for us no end of problems. Without going into these difficulties, I will describe the system as it stands today, practically perfect. The air is taken from a low point outside, where there is some sunlight, and led to the incubator by a three inch pipe, it passes through a cotton filter at the side of the lower chamber, passes beneath the water pan, under which it is spread by a curved plate, it is heated, and therefore rises through the flues at the side of the upper chamber.

It circulates downward around the infant, is collected under the bed, drawing off the odors from the child, and ascends through the flue at the head, escaping through a chimney from the top of the apparatus. A glass cylinder placed in this flue allows one to see the ventilator, or anemoscope, which indicates the current of air. Three feet above this chimney is a four inch air exhaust flue with an eight inch funnel. This creates a current from the floor of the nursery toward the ceiling, and is to check over strong down draughts into the incubator. It also carries out odors from the incubator. For hot, damp, muggy days, it may be necessary to aid the ventilation of the apparatus by modification of the intake of air from the outside, which problem will give little difficulty. The current through the incubator must be the gentlest possible, to give the infant enough air and yet not chill it with a draught. It is remarkable how sensitive these air currents are to even delicate fluctuations without. An incubator system cannot be operated successfully unless the air be taken fresh from outside. The air of hospitals is almost never good, and if heated is still worse for a delicate infant. The question of moisture is still being investigated. In the first place we lack a good hygrometer. We use the coil instrument standardized with Mason’s. Secondly, we lack knowledge of the amount of moisture an infant needs and of the amount it can tolerate when the air is at a high temperature. In ordinary room temperature of 65° to 70°, the relative humidity varies from 55 to 65 per cent. The amount of saturated aqueous vapor in a given space varies with the temperature, being small with hot air and large with cold. Thus the difficulty when the air of the incubator is heated up to 90° to 92° F. The relative humidity is reduced to 10 or 12 per cent unless artificial moisture is applied. This is done by passing the cold air over a wet screen, and, if necessary, by a small pan of hot water placed under the infant. The percentage of relative humidity best suited to infants is the subject of our study, and a report will be rendered later. At present we try to hold it between 35 and 50 per cent. A machine that will accomplish these functions is necessarily bulky, complicated and unwieldy to transport. A specially trained nurse is required to manage it, but such nurses are needed for the baby. The children had better, then, be sent to the hospital, which is usually advisable also for many economic reasons. The claim is made for this apparatus that it is an incubator built on scientific lines, and not a mere warm box. After the best regulator is once adjusted it needs no further attention. The ventilation is even and certain, and the moisture, with ordinary watchfulness, is held in normal degree. Like every important instrument it requires intelligent attention and care.