of problems, and still many of them feel satisfaction after having written a paper without many mistakes or having found the solution of a problem, and this in spite of the fact that they realize only later in life the necessity of this kind of intellectual training. I did not enjoy the study of English, French, and German while at school, and did not realize the necessity of this study; at present I thoroly appreciate the ability to read, study, and to deliver even this paper to you in a language which is not my own. But just as the lesson in geography, languages, etc., ought to be made as pleasant and interesting as possible, the teacher of gymnastics must know how to make his lesson attractive without, however, decreasing its beneficial influence on the physical development. It has been said also that the American boy does not like discipline and order and that, therefore, he ought to be taught in another way than the way in which the Swedish boy is taught. It would seem that, since a certain sense of discipline and order is a valuable quality for the American citizen as well as for anybody else, this quality ought to be developed, and the gymnastic lesson gives us a good opportunity to do this. It is clear that the favorable or injurious influences resulting from the different kinds of exercises will be most pronounced during the years passed in the school. The use of apparatus exercises as practiced in German and American gymnastics in the lessons for children cannot be defended by the mere fact that the most skilful among the boys enjoy this kind of exercises, since it is likely to produce harmful results on the hearts of the majority of the pupils. It is just the much-praised competitive element which, in German gymnastics, causes the child to do his utmost to perform a certain exercise, and, especially in the case of a strength exercise, this is not without danger. Trying to "chin" may put the same strain upon a child's heart as holding a lever for a trained gymnast. The particular attention given in "Swedish" gymnastics to a slow progression gives the best guaranty that the heart will not be overstrained. It has been said that the introduction of a more strictly corrective type of exercises would not succeed, because of the fact that the children "do not want that kind of stuff." This argument, however, is of no value. Why should the physical director make, during several years, a thoro study of anatomy, physiology, psychology, etc., if he is not to apply his knowledge on the gymnasium floor, the only place and the only moment that this knowledge can and ought to be of practical use? We must give the children the exercises that they need, not that they want; our study enables us to judge right—the children cannot do this themselves. I am exceedingly sorry that the time is too short to give you a complete outline of the Swedish system of gymnastics and to show you that its principles are in perfect harmony with the latest theories and with the results of the latest experiments in the line of physical education. All I can do at present is to give you my strong conviction, based on a thoro study of the different systems of physical education, that whatever may be, or may be claimed to be, wrong in the Swedish system of gymnastics, its principles are sound and true. I sincerely hope to see these principles adopted before long as the basis of physical education in American schools and universities. THE HEART VOLUME IN MAN-THE NITROUS OXIDE METHOD AND THE RESULTS OF PROFESSOR FRANZ MÜLLER ELMER BERRY, PROFESSOR OF PHYSIOLOGY, YOUNG MEN'S CHRISTIAN ASSOCIATION COLLEGE, SPRINGFIELD, MASS. The question of heart volume in man has recently been investigated by new methods and with fresh enthusiasm. It is the purpose of the following paper to report briefly on this recent work, particularly that of Professor Franz Müller, of the University of Berlin, with whom the writer has had the privilege of working as a student of his method and as a subject for experimentation in the Tierphysiologisches Institut der Landwirtschaftlichen Hochschule under the auspices of Geheimrat N. Zuntz. Reports on the nitrous oxide method have already appeared in German physiological publications,' and Professor Müller demonstrated the improved form of the method at the International Congress of Physiology held in Groningen, Holland, September 2–6, 1913. To the student of the physiology of exercise, no question is of more significance than that of the heart volume and the effect of exercise upon it. In the past the circulatory changes caused by exercise have been studied chiefly from the point of view of blood pressure and pulse frequency, tho some work has been done with the cardiograph, with the Roentgen rays, and on the circulation time. The real work done by the heart, however, must remain a supposition until the actual amount of blood delivered per beat or per unit of time is determined. The desire to measure the work of the heart has led to many attempts to estimate the heart volume. These attempts were at first based largely upon observations upon dogs. Vierordt, in a series of experiments on more than twenty dogs ranging in weight from 5 to 35 kilos, concluded that the output of the left ventricle per kilo of body weight diminishes as the size of the animal increases. If this same relation holds for man, a 70-kilo man would discharge about 80 cu. cm. of blood per heart beat. Considering this together with the circulation time, the conclusion is drawn that the average amount of blood thrown out by each ventricle at each beat is between 70 and 80 cu. cm. Zuntz, calculating from the quantity of oxygen absorbed by the blood in the lungs, has estimated the output at 60 cu. cm. He believes that this may be greatly increased during muscular work. In the middle 1 Zeitschrift für Balneologie und Klimatologie, Vol. IV (1911), Nos. 14 and 15. Stewart, Physiology, p. 127. of the last century Passavant calculated the output at 46.5 cu. cm. If these varying estimates, which are at best but rough approximations, differ so much for rest, what must the uncertainty be regarding the output during muscular work-the condition in which the physical director is primarily interested? GENERAL HISTORY A brief review of the older work may be helpful in showing the steps which have gradually led to the nitrous oxide method. First came the determination of the circulation time by Hering' and von Kries by introducing potassium-ferrocyanide into the central end of a vein and finding the time when it appeared in the peripheral end of the same vein. Frick devised a method of calculating the respiratory exchange, and from this the heart volume, by determining the difference in oxygen content of arterial and venous blood, the latter taken from the right auricle of the heart, making at the same time a determination of the total oxygen consumption of the animal. Following this method Gréhant and Quincaud carried out observations on dogs, and Zuntz with Hagemann3 made an extended research on horses. The results of this work agreed well with direct determinations made by Tigerstedt, who, following Ludwig, introduced a "Stromuhr" directly into the ascending aorta of rabbits. Bohr and Henriquez,5 however, showed that considerable oxidation might occur in the lung tissue itself and this oxygen would then appear in the arterial blood in a stable compound which could not be pumped out, thus invalidating the results. This objection, tho disputed," made it desirable to find a method less open to criticism and applicable to man. Loewy and von Schrötter? devised a method of calculating the tension of the gas in the blood indirectly from the gas tension in the lungs. For this purpose it was necessary to close a bronchus and give the air in that lung section time to acquire the same gas tension as the venous blood. Knowing this tension and the dissociation curve, the oxygen content of the venous blood could be calculated. This could then be compared with air from the free bronchi, giving the oxygen content of the arterial blood. The difficulty of the technic, however, 'Hering, Tiedemann, and Treviranus, Zeitschr. f. Physiologie, III, 85-1829. * von Kries, Verhältnis der maximalen zur mittleren Geschwindigkeit bei dem Strömen von Flüssigkeit in Röhren. Sep.-Abdruck. 3 Zuntz and Hagemann, Untersuch. über den Stoffwechsel d. Pferdes (Landro), Jahrbuch XXVII, Supplement I, p. 371. R. Tigerstedt, "Bestimmung der vom linken Herzen herausgetriebenen Blutmenge," Skand. Arch. f. Phys., III (1891), 145; “Die Geschwindigkeit des Blutes in den Arterien," Ergebn. d. Physiol., IV (1905), 481. s Bohr and Henriquez, Arch. de Physiol., nom. et pathol., V, Part IX, 459–74. "Plesch, Haemodynamische Studien (Berlin, 1909), pp. 130 ff.; Zuntz, Pflügers Arck., LV, 521. 7 Loewy and von Schrötter, Blutzirkulation beim Menschen (Berlin: Hirschwald, 1905). and its application only to therapeutic cases requiring bronchotomy made the method of no general use. Plesch, however, ingeniously modified this method so as to be usable by a normal breathing man. He used a gas bag and allowed the subject to breathe, for about thirty seconds, a gas mixture of low oxygen content so that its oxygen percentage after mixture with the residual air of the lungs would correspond approximately to the oxygen tension of the venous blood. If the oxygen tension of the mixture was above that of the blood going thru the lungs, oxygen would be absorbed; if lower, oxygen would be given up to the gas mixture. With the dissociation curve, the oxygen content could then be calculated. The dissociation curve of the oxyhaemoglobin, however, is not constant for all men. Barcroft' has shown that dyspnea and changes in CO, content in the blood may have a great influence on the dissociation curve, thus rendering the method unreliable, especially where work is concerned. It remained, therefore, still to develop a method applicable to workingmen.3 NITROGEN METHOD Bornstein, taking his cue from the work of Zuntz, hit upon the simple and ingenious idea of using an indifferent gas, choosing nitrogen. His principle is to breathe for a given time a gas of low nitrogen content (practically pure oxygen). As a result, nitrogen will be given off from the blood to this nitrogen-poor gas according to the relative nitrogen tension in the blood and gas. Knowing these tensions, the time of breathing, and the amount of nitrogen given off from the blood, the quantity of blood itself passing thru the lungs in the given time may be calculated and so the minute volume determined, and thus, knowing the pulse frequency, the pulse volume itself. The method is simple, requires comparatively little apparatus, and seems to give good results. The chief objection lies in the possibility that as the nitrogen disappears from the blood other nitrogen will be drawn from the tissues to the blood and so into the gas under observation. The nitrogen content of different tissues varies, Vernons having shown that fatty tissue may shelter even six times as much nitrogen as the same weight of blood or muscular tissue. Bornstein's method then furnishes a good means for comparative measurement on the same individual at rest. Barcroft and Camis, "The Dissociation Curve of Blood," Journal of Physiology, XXXIX (1909), 118; same with Orbeli, "Influence of Lactic Acid upon the Dissociation Curve of Blood," ibid., XLI (1910), 355; same, "Effect of Altitude on the Dissociation Curve of Blood,” ibid., XLII (1911), 145. 3 Bohr, Centralbl. f. Physiol., XVII (1904), 689. A. Bornstein, "Methode zur vergleichender Messung des Herzschlagvolumens beim Menschen," Pflügers Arch., CXXXII (1910), 307. s Vernon, Proceedings of the Royal Society, LXXIX (1907), 366. = It can be used for absolute measurements if the gas is not breathed longer than one circulation time. According to Bohr, blood has an absorption coefficient of 0.205 cu. cm. of N for 100 mm. tension of pure N; 100 divided by 0.205=488 cu. cm. of blood amount of blood used for 1 cu. cm. of nitrogen. If we find per minute and 100 mm. Hg. tension, a difference say of 10 cu. cm. of N, it equals 4,880 cu. cm. of blood. If the pulse is 62, the pulse volume=4,880 62 =78.7 cu. cm. The objection to Bornstein's method lies in the leakage of nitrogen from the tissues. A further objection is the unreliable results reported in work, where in some cases five to ten times as large a heart volume is found as in rest, while the oxygen consumption remains practically the same,' an obvious impossibility. NITROUS OXIDE METHOD The nitrous oxide method as used by Müller obviates this difficulty and gives absolute results in work. Nitrous oxide is a gas with a high absorption coefficient and follows the Boyle-Mariotte law in the body. Consequently it is necessary to breathe it only a short time to get good results (20-60 seconds)—an obvious advantage in work experiments. The first work along this line may be said to begin with an article published by Markoff, Müller, and Zuntz in 1910. Krogh and Lindhard, after extensive study, have also adopted nitrous oxide and independently, tho later than Müller, worked out a method for determining the heart volume. In general their method is similar to that used by Müller but apparently not so well worked out and not so free from technical errors. PRINCIPLE In principle the nitrous oxide method is exceedingly simple. A gas mixture containing known percentages of nitrogen, oxygen, and nitrous oxide is breathed for a given time. After the experiment, the resulting gas mixture is analyzed and the amount of nitrous oxide absorbed by the blood determined. Knowing the nitrous oxide absorbed, the absorption coefficient, and the time of the experiment, the amount of blood passing thru the lungs in this time may be calculated and so the minute volume determined. Then knowing the pulse frequency the pulse volume itself is given. In practice the experiment is divided into two parts: a preparatory part in which the subject breathes about 10 seconds, 2-4 breaths, from a spirometer containing about 25 per cent of nitrous oxide, and a principal part in which the subject breathes about 35 seconds, 3-5 breaths, from a spirometer containing about 18 per cent of nitrous 1 Zeitschrift d. Fortschritte der Medicin, January, 1912. 2 Veröffentlichungen der Zentralstelle für Balneologie, IV, 1–16. 3 Krogh and Lindhard, Skand. Arch. f. Phys., XXVII (1912), 100-125. |