heater it drops vertically until it gets below the basement floor level, where it enters the main 70x36 in. warm air duct, from which branches are run to the various hot air risers, as shown on Fig. 1, reaching the church, Sunday school and adjoining rooms as shown in Fig. 2. The exhaust ducts are also run under the basement floor to the fan located near the exhaust flue. This fan is likewise belt-driven from a similar motor and is of 120 in. in size with a 421⁄2 in. by 62 in. discharge and a 72 in. x 40 in. wheel, the motor being of 8 h. p. The Composition of the Air 1. Oxygen. It used to be assumed that the exact percentage of oxygen in the air was an important factor in determining the quantity of this element absorbed and used by the body. We now know that within certain rather wide limits the per cent. of oxygen has nothing to do with the case. The "margin of safety" (Meltzer) in the functioning of the oxygen taking and carrying apparatus is such that under any of the conditions found in ordinary life the amount of oxygen taken in and consumed is determined solely by the demands of the body, and not by the percentage in the air. A horse cannot drink any more out of a lake than he can out of a trough. The experimental data referred to show that the oxygen consumption of the body is not in any way affected by lessening the oxygen in the air till it has been reduced from 21% where it is normally, to about 15%. We also know that such to about 15%. We also know that such lowering of oxygen is never found except under the absolutely controlled conuitions of the laboratory. In other words a tight-shut school room full of pupils without any artificial ventilation will not suffer from lack of oxygen. They probably will suffer, but not from oxygen starvation. The exchange of gases through cracks in doors, windows, as well as through walls, floors and ceilings is so rapid as to maintain a practically uniform atmospheric balance in gases. 2. Carbon dioxide. We used to be told that this gas was a poison and even in minute quantities vitiated the air rendering it harmful for consumption. Later on we were told that while not proven to be harmful in very small percentages that it was our best measure of the extent to which air had been vitiated by breathing. Our present knowledge is to the effect that people may live in perfect comfort and health in an atmosphere so laden with this gas that a match will not burn in it. In this atmosphere their mental and physical faculties are entirely normal. They have no subjective way of knowing of the presence of the gas. 3. Organic Matter. In no field has physiological controversy been more active than with reference to organic matter in the expired air. The more refined methods of physical and chemical analysis possible under modern laboratory conditions have failed to show any organic matter in expired air. Rosenau's work alone appears to raise doubt but it is unsubstantiated and seems to be open to question by those most competent to speak on this topic. Organic matter is given off from decaying matter in the mouth, by pathological conditions in the nares and especially the posterior nares and from the skin. This may be harmful but does not constitute the "anthropo toxine" or "crowd poison" usually referred to. 4. Odors. Our evidence on this subject is mainly negative. It seems as if unpleasant odors should produce harm in proportion to their unpleasantness. We only know that we rapidly become habituated to such odors and so far, have not been able to trace any permanent direct result from them. Through arousing disgust-before habituation sets in physiological effects may be produced. In recirculating systems odors are rapidly removed by washing the air.-Dr. Luther H. Gulick before the International Congress on School Hygiene. On the Reinspiration of Expired Air UNIQUE EXPERIMENTS THAT CONFIRM THE THEORY OF THE HEAT ECONOMY OF THE BODY BEING THE IMPORTANT FEATURE IN VENTILATION. BY THOMAS R. CROWDER, M. D. (Presented before the American Medical Association, Chicago, Ill.) I desire to record a phenomenon and to discuss its significance. The phenomenon is, the immediate. 1einspiration of a portion of our expired air. This occurs quite commonly-so commonly, in fact, that it is an accompaniment of respiration during the major part of the lives of many people, and during a large part of the lives of practically all. The observation of this phenomenon is not new. Lehmann and Heymann have each reported a small group of experiments, in which they determined the carbon dioxide of the inspired air, compared this with the carbon dioxide of the surrounding air, and from the difference computed the proportion of the breath which was reinspired. The proportion varied greatly. It was sometimes more than 6%; it dropped to zero in the open air and in a breeze of 3 meters per second. A few years ago this subject attracted my attention in connection with certain studies of ventilation. The experiments of Lehmann and Heymann demonstrated little except that reinspiration may and does occur. It seemed desirable to carry the observations further. As opportunity arose this has been done, and an attempt has been made to determine some of the factors controlling this phenomenon. The work has included the analysis of about 900 samples of inspired air. METHODS In order to find what proportion of the expired air re-enters the respiratory tract with the succeeding inspiration, it is necessary to collect samples of the inspired air as it enters the nasal passages and subject them to analysis. The only difficulty in collecting the samples arises through the possibility of including a portion of the expired air as it leaves the nasal passages. This is likely to occur if the taking of the sample is not accurately timed to the inspiratory period; collection must begin after inspiration is established and must end before expiration has begun. Experiments such as these are more readily carried out on oneself than on a second person, because of the easier identification of the respiratory periods. With a little practice one may become perfectly conscious of the beginning and end of inspiration; and with a little more practice may learn to bring the inlet tube of a bellows into the nasal orifice at the proper moment and to remove it at the proper moment, using one hand meanwhile to manipulate the bellows. By arranging for an air current that will immediately carry away all of the expired air, a series of controls may be run that will show clearly when the technic is mastered. The observations herewith recorded were made by the author on himself. Those made by the experimenters above referred to were made on a second person. After various trials of more or less complicated apparatus, a very simple. plan of collecting samples was adopted. The ordinary Paquelin cautery bulb was found to answer very well for this purpose after a little alteration. The only necessary alterations are a long rubber tube with a glass tip attached to the bellows intake, and a pinch-cock applied to the outlet tube from the elastic bag. A somewhat larger and heavier bag than that ordinarily supplied with the cautery was used, but the arrangement was essentially the same. The accompanying photograph (Fig. 1) shows the apparatus used, and the case for collecting and carrying samples and records. A is the intake tube, B is the bellows, B' the elastic bag and O the outlet tube." After inspiration is well established the glass inlet tube is brought just within the nasal orifice or between the parted lips during mouth breathing-and the bellows given two or three quick compressions. The inlet tube is removed during expira by a very simple computation, based on the fact that the expired air contains about 450 volumes of CO, in 10,000 volumes of air. It will, of course, vary a little from this figure, which is an average, but the variation will be relatively small and will affect the computation only slightly. It should be remembered that the normal air contains 3.5 to 4 parts of CO2 per 10,000. All above this is contamination, the result of respiration, burning lights, or other chemical processes. In the majority of instances all CO2 above 4 per 10,000 represents respiratory contamination; and in a broad sense all CO2 FIG. 1.-APPARATUS USED IN COLLECTING SAMPLES OF AIR. A, intake tube: B, bellows; B', the elastic bag; 0, outlet tube. tion and is again brought into place during the succeeding inspiration. This is repeated during eight or ten breaths, or until about 1.000 cubic centimeters of air have been collected in the bag. The outlet tube is then thrust to the bottom of a 2-oz. bottle and the air run through it by releasing the pinch-cock. This leaves the sample of air in the bottle. On withdrawal of the tube a waxed glass stopper is inserted and the seal made perfect. If the bottle is clean and dry there will be no change in the air it contains for a fortnight or more. The samples are then transferred under a saturated solution of sodium chloride to a Petterson-Palmquist apparatus and analyzed for carbon dioxide. At the time the samples of inspired air are collected, samples of the surrounding air must also be taken. The amount of immediate reinspiration is measured by the difference in the carbon dioxide content of these two. In the accompanying charts this difference is shown directly, and the proportion of CO, in the air is expressed in ten-thousandths of the whole volume. In the text, reinspiration is referred to in terms of per cent.; that is, the proportion of expired air which is mixed with the inspired air and which is therefore reinhaled after it has been once expelled. It may be assumed that for every 4.5 per 10,000 difference between the CO, of the inspired air and of the surrounding air, 1% of the expired air is being reinspired. This is derived above 4 per 10,000 in the inspired air generally represents reinspiration. But for our present purpose we shall consider only the CO, which is in excess of the amount contained in the general surrounding air; for it is this portion only which represents that strictly local contamination which leads to the immediate reinspiration of our exhalations now under discussion. RESULTS 2 It was soon noticed that, under apparently fixed conditions, repeated observations of the inspired air would always show considerable variation in the CO, content. All experiments were therefore carried out with serial tests, including from 4 to 24 successive samples, in order to arrive at averages. The individual observations of such series can be made at about one minute intervals when one is standing or sitting. They will fall a little farther apart when lying down, or under any circumstances which occasion interference with the easy manipulation of the apparatus and the records. It proved desirable to alter the surrounding conditions, especially amount of ventilation, at the same time and place, or to induce artificial air currents, and observe the effects on the phenomenon under investigation by running parallel series of tests. The effect of changes of position, body motion, different types of breathing, different temperatures and different degrees of contamination of the surrounding air were also investigated; and finally, the question of whether or not reinspiration takes place in such half-sheltered places as the sleeping-porch and in the open air. The results will follow in order. Unless otherwise specified, nasal breathing is referred to. THE AIR ABOUT THE FACE If the conditions are such that reinspiration can take place, the air about the face will necessarily be found to contain more CO2 than the surrounding air. It is on the fact that the expired air is not immediately removed or disseminated that reinspiration depends. That it remains about the face for an appreciable interval, is easily demonstrated. This is illustrated in Fig. 2. The heavy horizontal line in this, as in the general air of the room. It was constant to within half a point of 4.5 per 10,000. This half a point in 10,000, or 1 in 20,000, may be considered as about the maximum necessary error of the determinations. The series of samples represented by the upper curve, marked A, were taken close to the nose while holding the breath at the end of normal expiration; they contain an average of 3.8% of expired air. Those represented by the lower curve, marked B, were taken at the same place while holding the breath at the end of normal inspiration; they contain an average of 0.9% of expired air. The time occupied in collecting each of these samples was about five seconds. Those represented by the middle curve, marked C, were taken from within the nasal orifice during inspiration; they, therefore, show the contamination of the inspired air, which averaged 7.5 more CO2 per 10,000 than was contained in the air of the room. This excess of CO2 represents 1.7% of expired air; we therefore have for this series 1.7% of reinspiration. The average for each series is shown by the short horizontal line at the right. This experiment was carried out while sitting in a well-ventilated room of 3,000 cu. ft. capacity, having three windows and three doors. The temperature was 73°F. A little variation of the last experiment will show that this local contamination reaches a considerable distance below the face, and that it decreases with increasing distance. Fig. 3 illustrates some of the results with such a variation. At 4 is shown a series of samples taken close to the body and 6 to 8 in. below the nose during expiration; they contain an average of 4.6% of expired air. At B is shown a series taken 12 to 15 in. below the nose during expiration, and they contain 2.8% of expired air. At C the samples were taken 6 to 8 in. below the nose during inspiration, and contain 0.7% of expired air. At D the samples were taken 12 to 15 in. below the nose during inspiration, and the contamination amounts to only 0.1% of expired air. These tests were made in the same room as the above, when there was a measured air-supply in excess of 15,000 cu. ft. per hour entering through an open transom. The conditions noted in Figs. 2 and 3 are fundamental to our investigation. The contamination may be traced further; it tends to disappear rapidly, both in the time and space relation. The general facts are not particularly new or strange. They may be roughly determined by any one who will watch the course of smoke blown through the nostrils. THE EFFECT OF TEMPERATURE It has been sometimes stated before scientific bodies that when the surround 28 26 of which lies quite close to the body, and that convection currents tend to carry this part upward over the face. Inspiration succeeds expiration almost immediately; any upward current would therefore have to be very rapid in order to carry this air away before the latter process begins. Convection currents caused by the heat of the body, instead of being rapid, are just the opposite. That reinspiration undoubtedly does 60°F. will be seen from the two series take place at temperatures much below of observations illustrated in Fig. 4. That at the left was made in a large room of 16,000 cu. ft., with windows on three sides. It had a temperature of 50°F., and the reinspiration averaged 2.1%. That at the right was made in a small FIG. 3.-(EXPS. 8 AND 9). SHOWING CONTAMINATION OF THE AIR 6 TO 8 IN. AND 12 TO. 15 IN. BELOW THE NOSE DURING EXPIRATION (A AND B), AND AT THE SAME PLACES DURING INSPIRATION (C AND D). ing air is cool-below 60° F. or thereabouts-the expired air will rise out of the breathing zone on account of its lower specific gravity, and reinspiration will not take place. The results shown in the last chart would seem to cast a doubt on the theoretical correctness of this view. Those making the statement have failed to consider the downward propulsion of the expired air from the nares, that it takes on a cone-shaped expansion, a part FIG. 4.-(EXPS. 24 AND 27). SHOWING THE INSPIRED AIR WHILE STANDING IN A ROOM OF 16,000 CU. FT. AT 50° F. (AT THE LEFT), AND IN A ROOM OF 1,500 CU. FT. AT 43° F. (AT THE RIGHT). room of 1,500 cu. ft. The temperature was 43°F. and the reinspiration also averaged 2.1%. If a low temperature has any effect it tends to increase reinspiration. Within certain limits I believe that it does this, though I am not prepared to show that it has any constantly appreciable effect. Fig. 5 shows an attempt to make the comparison in a cold and in a warm air with. otherwise uniform conditions. The experiment was carried out in a small bed |