Vierordt, 1845

The next two contributions to the experimental research on the respiratory exchange as affected by the ingestion of food unfortunately deal with a very imperfect method for both sampling and analyzing the expired air. Vierordt,1 in making a very large number of observations on himself, employed a mouthpiece consisting of a short tube over which the lips closed. The nostrils were not closed during the experiment, as Vierordt thought it was impossible to breathe simultaneously through nose and mouth during quiet, normal respiration. The expired air was collected in a glass vessel containing 9,200 c.c, which was filled with a solution of common salt. About 1 1/2 minutes were required to fill this vessel completely with expired air. Vierordt based his carbon-dioxide measurements on 1-minute periods, making two experiments in an hour. A mixed diet was taken in the food experiments. Of special interest in this connection are the comparisons made by Vierordt between the food experiments and the fasting experiments. On two occasions when he had not eaten since 7 a. m., he obtained values while still fasting at 2 p. m. He compares the average of these two fasting experiments with the average of his experiments made at 2 p. m. just after eating. This comparison is shown in table 1.

Table 1. - Comparison Of Results Obtained During Fast And After Food (Vierordt)

(Values per minute).

From other experiments made when meals were taken at different times of the day, he concludes that the digestion of the evening meal proceeds with less energy than that of the noon meal. His conclusion is in part borne out by the fact that the pulse after the evening meal did not show the marked rise which was found after the noon meal.

1Vierordt, Physiologie des Athmens, 1845.

Although Vierordt's methods of sampling and analysis seem very crude, we find that Speck, 47 years later, quotes Vierordt as obtaining values not at all unlike those obtained by himself;1 in fact, he confirms Vierordt's observations in that he finds the maximum carbon-dioxide excretion about 1 hour after the meal.

Bocker, 1849

Although Vierordt was on two occasions able to compare directly the values obtained before eating with those obtained immediately after the meal, in the extensive research published by Bocker2 in 1849 no data were obtained for the post-absorptive condition. His experiments, which were carried out with exactly the same technique as that of Vierordt, are very extended and include the ingestion of sugar, which was taken in portions usually of 1 to 3 ounces, i. 6., about 30 to 90 grams. Occasionally it was taken with honey, but usually with water.

The method of computation employed by Bocker is somewhat difficult to follow, for while the percentage of carbon dioxide in the expired air found by him is not unlike that commonly found, namely, 3.5 per cent, the absolute amount of carbon dioxide excreted per minute is considerably more than that ordinarily found under like conditions, varying in his own case from 445 to 589 c.c. per minute. These results were obtained by multiplying the actual values found by the factor 2.51. The found values are much more in accordance with those commonly experienced, namely, from 177 to 235 c.c, than those obtained by means of the factor.

From these imperfect experiments Bocker concludes that after the ingestion of sugar the amount of carbon dioxide produced is decreased in the ratio of 571.35 to 540.58. He records a marked increase in pulse rate after sugar ingestion. In a series of experiments made with coffee he concludes that the taking of coffee decreases both extensively and intensively the respiratory processes. In discussing the pulse rate Bocker states that he does not think there is any necessary connection between the increase or decrease in pulse rate and the increase or decrease in the production of carbon dioxide, nor does he think that the changes in the respiration rate cause a change in the carbon-dioxide production. From a series of experiments on alcohol he concludes that alcohol decreases both intensively and extensively the respiratory processes.

Smith, 1859

Next to the few classical experiments of Lavoisier and Seguin no early research is more justly and frequently cited than is that of Edward Smith, who published two papers in 1859. In the first paper3 he describes in detail his methods of experimentation. A mask with two valves was used, the inspired air passing through a dry gas meter, and the expired air passing first through vessels containing sulphuric acid and finally through a strong solution of caustic potash to absorb the carbon dioxide. The amount of carbon dioxide exhaled was found by weighing, the total amount of ventilation being determined from the volume of air passing through the dry gas-meter. In practically all of the experiments the subject was in the sitting position. A large number of tests were made, both without and with food. In most of the food experiments a substantial mixed diet was used. In giving his results, Smith unfortunately expressed the excretion of carbon dioxide in English grains per minute,1 but a large proportion of the original data has been recomputed by Sonden and Tigerstedt to grams per minute,2 and presented in their excellent collection of the literature of early metabolism experiments. The average of the experiments made on himself and with three other subjects showed approximately 8.78 grains of carbon dioxide per minute for an 18-hour day with 3 to 4 meals. As the data obtained in the experiments without food gave an average value of 6.64 grains per minute, the increment after food would be 2.14 grains of carbon dioxide per minute, or 32 per cent over the fasting condition. In one observation Smith took 500 grains of arrowroot boiled in water, and found a slight increment over the fasting value. Generally the maximum quantity of carbon dioxide was observed in from 1 to 2 hours after the meal.

1Speck, Physiologie des menschlichen Athmens, 1892, p. 36. 2Bocker, Beitrage sur Heilkunde. 1849, 1. 3Smith, Phil. Trans., 1859, 149, p. 681.

Since Smith found, in his first paper, that the processes of digestion with a mixed diet increased the metabolism by approximately 33 per cent, he planned the experiments reported in his second article3 for the especial purpose of studying pure food materials. A large number of food materials of all classes were studied. Certain of Smith's conclusions are recorded herewith:

"It is evident that foods may be fitly divided into two classes, viz., those which excite certain respiratory changes (excito-respiratory), and those which do not. The excito-respiratory are nitrogenous foods, milk and its components, sugars, rum, beer, stout, the cereals, and potato. The non-exciters are starch, fat, certain alcoholic compounds, the volatile elements of wines and spirits, and coffee leaves.

"Respiratory excitants have a temporary action; but the action of most of ihem commences very quickly and attains its maximum within one hour.

"The most powerful respiratory excitants are tea and sugar; then coffee, rum, milk, cocoa, ales, and chicory; then casein and gluten, and lastly, gelatin and albumen. The amount of action was not in uniform proportion to their quantity. Compound aliments, as the cereals containing several of these substances, have an action greater than that of any of their elements."4

We can not conclude the discussion of this interesting memoir of Smith's without noting that he recognized at this early stage of research some important factors which are considered at the present time as practically indispensable for successful respiration experiments. Thus, he says that there was always a short period of rest before the observations began. He states:

115.432 grains equal 1 gram.

2Sonden and Tigerstedt, Skand. Arch. £. Physiol., 1895, 6, pp. 101 and 143.

3Smith, Phil. Trans., 1859, 149, p. 715.

4Ibid., pp. 738-739.

"We sat down at least a quarter of an hour before taking the first observation, or that which showed the state of the system before the substance under inquiry was taken, and which was the basal state with which the subsequent effects of the substance were compared, and upon the accuracy of which the truthfulness of the results mainly depended."1

That he recognized the importance of quietness and uniform muscular activity is indicated by the statement: "the same conditions as to posture and quietude being maintained unbroken throughout the whole inquiry." Finally, we may cite one of the conclusions from his first paper:

"There is a normal or basal line below which the system does not pass in health and wakefulness, and which is tolerably uniform. It is the same in the complete abstinence from food as at the end of the interval between meals. There is, also, when at rest, a higher point, which the system does not exceed, due to food, and it is the highest after breakfast and tea."2