Lavoisier And Seguin, 1789

The fact that the ingestion of food causes an increase in the metabolism in the body was first made known through the classical researches of Lavoisier and Seguin.1 As with many phases of physiological chemistry, our first information as to quantitative values for these important body processes is obtained from the remarkable series of experiments carried out by Lavoisier. Judging from incomplete statements appearing intermittently in the writings of Lavoisier and of Seguin, together with the drawings attributed to Madame Lavoisier, the expired air was collected by means of an air-tight mask attached to the subject's face. It is of interest to note that this method is now the basis of practically all of the modern mine-rescue apparatus and "gas-masks", and is also finding extensive use in clinical laboratories.

The statement is made by Lavoisier that a man fasting, or at least with an empty stomach and quiet, consumes in one hour 1,210 cubic pouces of oxygen. This corresponds, according to the table of reductions of Gavarret,2 to 24.002 liters. Lavoisier also states that during digestion the oxygen consumption increases to 1,800 or 1,900 cubic pouces, the latter value corresponding to 37.689 liters. Thus we note an increment of approximately 700 cubic pouces due to taking food or, in other words, somewhat over 50 per cent. The kind of food and the amount eaten were not given. Lavoisier recognized the fact that individuality may play a role here; we cite his criticism:

"Nous ne parlons en ce moment que de rapports. On concoit, en effet, que la consommation absolue doit varier considerablement dans differents indi-vidus, suivant leur age, leur etat de vigueur et de sante, suivant qu'ils ont plus ou moins contracte 1'habitude des travaux penibles; mais il n'est pas moins vrai qu'il existe pour chaque personne une loi qui ne se dement pas, lorsque les experiences sont faites dans les memes circonstances et a des intervalles de temps peu eloignes."3

In studying the literature 130 years after the appearance of Lavoisier's first paper, it is surprising to note his clear conceptions of the problems involved both in the muscular work of man and in digestion. While an increment in metabolism amounting approximately to over 50 per cent is somewhat higher than that commonly observed and somewhat higher, in all probability, than modern methods would show for the diet of the subject, nevertheless it is by no means an impossibility. We have thus this earliest recorded estimate of the increased energy required to digest a meal.

1Seguin and Lavoisier, Memoires del'Acad. des Sciences, 1789, p. 185; also Oeuvres de Lavoisier, 1862, 2, p. 688. 2Gavarret, Physique medicale. De la chaleur produite par les etres vivants. 1855, p. 330. 3Seguin and Lavoisier, Oeuvres de Lavoisier, 1862, 2, p. 696.

Jurine, 1789

Almost simultaneously with Lavoisier's paper we have an interesting communication from Jurine of Geneva. In his researches Jurine employed a Fontana eudiometer, then much used in Europe as the earliest method for analyzing gases, particularly atmospheric air. With this apparatus he studied the influence upon the expired air of various physiological processes, among others those of the ingestion of food.1 The experiments were confined exclusively to determinations of the differences in composition of the expired air. The subject evidently breathed through a glass tube flattened to fit the shape of the mouth, and the expired air was collected at times over water and at times over mercury in a bell-jar. A stopcock was turned at the beginning and end of each expiration. Among other experiments, Jurine made three on the influence of food upon the respiratory exchange as shown by the changes in the composition of the air. Both a fasting experiment and a food experiment were made with each of three subjects, a young girl 10 years old, a man 36 years old, and a woman 62 years old. The food experiments were to determine if the increased blood circulation, depending on or incident to digestion, would increase the oxygen consumption. In the air collected over water no change was found in the oxygen content, while in the air collected over mercury a very sensible increase was found in the proportion of carbon dioxide present. The total amount of carbon dioxide produced in 24 hours was computed by Jurine from the average number of respirations and from the volume expired per respiration. We find no evidence, however, that he calculated the total increase in the carbon-dioxide production due to digestion.

This method of studying the expired air was followed for a number of years by other scientists, little emphasis being placed upon the total quantitative amount of carbon dioxide expired in a given time, but chiefly upon the alteration in the carbon-dioxide content of the expired air. We know now that this change in composition has but little significance unless accompanied by some knowledge of the total ventilation of the lungs, a factor that was entirely overlooked, or at least undetermined, in many of the early researches.

Prout, 1813

One of the most extended observations upon the influence of food on the carbon-dioxide percentage of the expired air is that recorded by Prout.2 The subject, Prout himself, expired into a bladder, regulating the number of expirations to six. A sample of air was then taken in a tube and the carbon dioxide was determined by absorption with strong caustic potash. Prout remarks that as his main object was to discover general laws he did not pay so much attention to the question of the influence of food, although during the three weeks of experimentation he ate only the simplest food and with as much regularity as possible. The effects from the food, therefore, were not remarkable. Apparently the food taken simply kept the carbon-dioxide production up to the standard and occasionally increased it somewhat, certainly never depressed it. Prout found that fermented liquor, which was occasionally taken, always depressed the carbon-dioxide production. Tea had a like depressing effect, for after 3 or 4 ounces of strong, cold tea he found a considerable diminution in the carbon-dioxide produced. As Prout was much surprised to note the depressing effect of alcohol and all liquors containing it, he made a number of observations on alcoholic liquors, which invariably gave the same result, i. e., a depression of the carbon-dioxide excretion. In this consideration of his results, it is important to bear in mind the fact that his observations were solely on the percentage of carbon dioxide in the air. Little evidence is given in this paper to lead one to think that he had any conception of the total amount of the carbon-dioxide excretion. Scharling,1 in citing Prout's experiments, concludes from the figures given for pulse rate that there really was a greater carbon-dioxide production after the ingestion of food than Prout noted.

1Jurine, Histoire et Mem. Soc. Med., 1789,10, p. 19. 2Prout, Annals of Philosophy. 1813, 2d ed., 2, p. 328.