1 The "lying" periods were all run on another respiration apparatus located on the third floor of the laboratory. The subject went downstairs to the first floor for the work periods and then returned to the third floor. The ventilation of the lungs was measured while the subject was on the couch. 2 The respiration rate while the subject was on the couch was for the full period, as recorded by the spirometer. 3 The subject said at the close of this period that he had a headache. His forehead was bathed in perspiration. 4 Work was started at 9h 57m a.m. Between 9h 57m a.m. and 10h 11m a.m. the average speed was 104 revolutions per minute. 5 Between the periods the average speed was 82 revolutions per minute. 6 Work was finished at 10h 55m a.m. The subject immediately left the ergometer, hurried upstairs, and lay down on the couch. 1 The metronome was used in each period to regulate the speed. 2 Work was begun at 8h 06m a.m. Between 8h 06m a.m. and 8h 43m a.m. the average speed was 70 revolutions per minute. During the period the work was done with perfect ease. There was no strain whatever. The subject said he scarcely felt the work. He said he had been at Revere Beach on Apr. 7 and had ridden 10 miles on the track at the rate of 1 min. 36 sec. to the mile. He had done this with absolutely no difficulty. His opinion was that one hour's work on the ergometer was equivalent to about 50 miles on the track. 3 In the interval before this period the average speed was 66 revolutions per minute. work was done without difficulty. 4 In the interval before this period the average speed was 70 revolutions per minute. work was done with ease. During the period the 5 At 9h 45m a.m. the speed was increased to 120 revolutions per minute. Between 9h 45m a.m. and 10h 12m a.m. the average speed was 90 revolutions per minute. During the period itself the work was done at tremendous speed toward the end. At the end of 7.5 minutes the subject lost a pedal and picked it up again. Perspiration was not very profuse. 6 In the interval before this period the average speed was 76 revolutions per minute. During the period the work was done with greater difficulty. The subject found it harder. Perspiration was very profuse. 7 The pulse was very rapid in this period, no satisfactory count being possible. 8 In the interval before this period the average speed was 70 revolutions per minute. During the period the work was done with comparative ease. It was much less trying than in the preceding period. 9 Pulse-rate at the end of the period. 1 Work was begun at 8h 18m a.m. Between 8h 18m a.m. and 8h 56m a.m. the subject rode at the average rate of 70 revolutions per minute. During the period the work was very easily done, in fact it could hardly be considered work. There was no perspiration. 2 In the interval before this period the average speed was 71 revolutions per minute. There was slight perspiration during the period. 3 In the interval before this period the average speed was 71 revolutions per minute. The perspiration was somewhat increased. 4 At 9h 55m a.m. the speed was increased so that between 9h 55m a.m. and 10b 21m a.m. the average rate was 97 revolutions per minute. At the beginning of the period itself the subject lost the pedals, otherwise the speed during the period would have been greater. The work was hard and perspiration was profuse. 5 Pulse-rate at the end of the period. 6 In the interval before this period the average speed was 74 revolutions per minute. During the period perspiration was very profuse. The subject was practically "all in" at the end of 8 minutes, but kept at work. He looked very tired and exhausted. He was so tired that for about the first time since he had worked here he could not go on and asked to be relieved from doing a third period at this resistance. He said that the rapid pace of the first high speed period had killed him. 1 This experiment was to a certain extent an attempt to learn the after-effect of work on the respiratory metabolism. 2 The "lying" periods were carried out on another respiration apparatus located on the third floor of the laboratory. The work periods were as usual with the apparatus on the first floor. 3 The respiration rate while the subject was on the couch was for the full period, as recorded by the spirometer. 4 The subject had considerable trouble just at the end of this period. He said that he had pain in his throat and difficulty in breathing. The kymograph record shows disturbance, the respiration becoming very irregular. 6 Work was begun at 9h 48m a.m. Between 9h 48m a.m. and 10h 08m a.m. the average speed was 99 revolutions per minute. During the period the work was easily done, except that the subject was troubled by a tendency for his feet to slip from the pedals, as just after starting he broke his toe-clips. He looked very well. 6 Between the periods the average speed was 84 revolutions per minute. During the second period the work was still readily done. 7 Work was finished at 11h 03m a.m. and the subject immediately went upstairs to the third floor and lay down on the couch. 8 The subject said he was becoming very tired and stiff with lying. He was also very hungry. He moved his legs freely before the period started. PART III. DISCUSSION OF RESULTS. The mass of experimental data accumulated in connection with this research permits of the adequate discussion of several major and innumerable minor problems in the relationship between muscular work and metabolism. We shall lay our greatest stress upon a consideration of the character of the katabolism and the mechanical efficiency of the body, and finally devote a portion of the discussion to a presentation of our evidence bearing upon a number of the physiological effects of muscular work. THE CHARACTER OF THE KATABOLISM AS AFFECTED BY MUSCULAR WORK. When muscular work is performed by the human body, the consumption of fuel either from food or from body-material is greatly increased. When food is not given, the energy must be supplied from body-material. If we consider to what extent, under these conditions, the constituents of the bodymaterial are available for the production of energy, we find that the amount of protein present in the normal human body is amply sufficient to provide for all drains upon nitrogenous material during rest or a short period of work. Similarly, with a well-nourished man there is a practically unlimited supply of fat. On the other hand the supply of carbohydrates is found to be very limited; thus, with dogs and with other animals, it is possible to rid the body of all but traces of glycogen by starvation, by strychnine convulsions, and by the shivering induced by prolonged exposure to severe cold, while under the same conditions there is no material draft upon the body-protein and but a small part of the large amount of body-fat is used. Apparently the storage of carbohydrates is also somewhat easily depleted by excessive muscular work. It is believed, therefore, that the ideal conditions for a study of the question as to whether or not there is a selective combustion of carbohydrate material during severe muscular work would obtain after the subject had abstained from food for twelve to fifteen hours, i.e., when there was a relatively large supply of body-protein, and a relatively small supply of bodyglycogen. If, under these conditions, a selective combustion took place, the supply of body-glycogen would be rapidly depleted and this would be indicated by the respiratory quotient. Nearly all of our experiments, therefore, including both the rest and the work experiments, were made in the morning, the subject having taken no food since the previous evening. We have found it difficult to select a word to express this condition of abstinence from food for 12 hours. As is well known, the stimulating action of the substances absorbed from recently-introduced foodstuffs produces an increase in total katabolism which frequently obscures the effect to be studied. A German word, "nüchtern," has been freely used in the past but in our opinion it is not explanatory. English words, such as fasting, breakfastless, etc., have been considered but owing to difficulties in connection 71 with the common use of these words, they are unsuitable. We prefer the far-reaching term post-absorptive. We were fortunate in being able to secure a subject who was not made unduly uncomfortable by performing a large amount of muscular work on an empty stomach, so that in neither the rest nor the work experiments were the measurements of the metabolism complicated by the influence of food. While it cannot properly be said that during the experiments the entire alimentary tract was free from absorbable material, nevertheless, it was to a very large extent thus free, so that for all practical purposes we may say that the subject was living upon body-material. By previous experimenting in this laboratory, it has been shown that the character of the post-absorptive katabolism might be considerably modified by normal alterations in the diet. It was therefore necessary to obtain a baseline both for the character of the katabolism as shown by the respiratory quotient and for the amount of the katabolism as determined by the measurement of the carbon dioxide produced and the oxygen consumed. This base line was determined by making a series of rest experiments each morning previous to the experiment with muscular work. In order that the picture of the resting katabolism might be more complete, an attempt was made to secure regularly the urine voided during the experimental period. In a research of this kind it is of course necessary to assume that the nitrogenous products of the urine collected during an experimental period represent the protein disintegration for that period. This assumption is liable to many gross errors, particularly in experiments with severe muscular work as an after-effect of the work upon protein katabolism, or at least the nitrogenous excretion in the urine, has frequently been noticed. Analyses have been made of these urines, however, and the results of the determinations are reported. DETERMINATION OF THE RESPIRATORY QUOTIENT. In a study of the character of the katabolism as influenced by muscular work, the significance of the respiratory quotient makes it necessary that this value should be determined with the greatest accuracy. This is doubly difficult inasmuch as the determination of the respiratory quotient is affected by errors in the values obtained for both the carbon dioxide and the oxygen. The determination of the carbon dioxide produced by man is relatively a simple matter, there being a number of excellent methods for this purpose. The determination of the oxygen absorption is, on the other hand, very difficult, and while several methods are in good repute among physiologists, it still remains a fact that extraordinary skill is required on the part of the observer to secure reliable results. All of our energies, therefore, were concentrated in an effort to obtain the most exact measurements of these two factors. The determinations of the carbon dioxide and the oxygen were always verified, the respiration apparatus and the connections with the subject were continually tested for tightness, precautions were taken to insure the full efficiency of the absorbers, and the calibrations of the meter were often checked. Furthermore, the inherent difficulties involved in an altered respiratory type and the possible effect of a pumping out of carbon dioxide by excessive ventilation were taken into consideration. ERRORS INCIDENTAL TO THE DETERMINATION OF THE CARBON-DIOXIDE PRODUCTION. In the type of apparatus here used the carbon-dioxide production is determined by absorbing the gas in suitable containers filled with soda-lime. No volumetric gas-analyses, no aliquoting of samples, and no records of the variations in the barometer and the pressure are required. The determination of the carbon dioxide in the air-current thus becomes a method of gravimetric analysis. There are, however, several possible sources of error. The first to be considered is an incomplete absorption of the carbon dioxide due to the inefficiency of the soda-lime. To provide for the absorption of any excess of carbon dioxide the air was swept through the system for several minutes at the end of each experimental period, the air-current passing through the soda-lime two, three or even four times. Furthermore, a test of the air leaving the soda-lime bottles was frequently made by passing a small sample of it through barium hydroxide, the complete absorption of the carbon dioxide being shown by the absence of turbidity. We have also found an annoying source of error in the fact that when the absorbers are weighed, the rubber gaskets used to secure tight closure between the different receptacles are occasionally left in the couplings. Each weighing of the soda-lime bottles was therefore checked by a second person and the absence of the gasket noted on the record sheet when the record of the weight was made, thus eliminating the possibility of error from this cause. Another way in which the determinations of the carbon dioxide may be affected is by the inefficiency of the sulphuric acid in the air-drying bottle. If, through carelessness, the sulphuric acid in this bottle is allowed to absorb more than 10 grams of the water taken up in the passage of the air through the soda-lime, the absorption will not be quantitative and the determined amount of carbon dioxide will be lower than that actually produced. To provide against this error, it was the custom to have the two soda-lime bottles and the air-drying bottle removed at the end of each day's experiment, repeated tests having shown that the limit of absorption, namely, 10 grams, was never reached under these conditions. In view of these precautions, we have every confidence in the measurements of the carbon-dioxide production." ERRORS INCIDENTAL TO THE DETERMINATION OF THE OXYGEN CONSUMPTION. The determination of the oxygen consumption can be made either gravimetrically, as was originally designed for this apparatus, by weighing the oxygen cylinder before and after the experiment and noting the amount of oxygen added to the air-current, or by the more convenient and recently adopted method of measuring the amount of oxygen by means of a carefully calibrated Bohr gas-meter immersed in water. This method of measuring the oxygen consumption depends upon the fact that the subject uses out of the air in the system a certain amount of oxygen which must be replaced by pure oxygen or by a known volume of some other gas. If the oxygen in the system is not allowed to fall below 10 or 11 per cent, even pure nitrogen might be used to replace the oxygen absorbed and bring the air to the original volume, since it has been shown that the metabolism is normal above this oxygen percentage. For this replacement, however, we ordinarily use oxygen a More recent tests kindly carried out by Mr. T. M. Carpenter have shown conclusively that no appreciable amount of water escaped absorption. |