August 1 6, 1888] 



NATURE 



379 



In 1809 the subject of aquatic breathing was investigated with 

 great care by Provencal and Humboldt. They collected and 

 analyzed the gases of water before and after fishes had lived in it 

 for a certain time, and showed that oxygen was consumed and 

 carbonic acid produced by these creatures. 



We have now seen how gradually knowledge was arrived at as 

 to the respiratory exchanges. At the beginning of the present 

 century it was recognized that expired air had lost oxygen, 

 gained carbonic acid and aqueous vapour, and had become 

 hotter. Since then many researches have been carried on to 

 determine with accuracy the quantities of these substances. In 

 all of these, as shown in these diagrams, 1 the method followed 

 has been to draw through a chamber containing the animal a 

 steady constant stream of air, the quantity and composition of 

 which is known. Thus, suppose a certain quantity of dry air, 

 free from carbonic acid, and consisting only of oxygen and 

 nitrogen, is passed through such a chamber. In the chamber 

 some of the oxygen is consumed, and a certain amount of 

 carbonic acid and of aqueous vapour is given up by the animal. 

 The air is drawn onwards through bulbs or glass tubes contain- 

 ing sub-tances such as baryta-water, to absorb the carbonic acid, 

 and chloride of calcium or sulphuric acid, to absorb the aqueous 

 vapour. It is evident that the increased weight of these bulbs 

 and tubes, after the experiment has gone on for some time, will 

 give the amounts of carbonic acid and aqueous vapour formed. 

 Thus Andral and Gavarret in 1843, Vierordt in 1845, Regnault 

 and Keiset in 1849, von Pettenkofer in i860, and Angus Smith 

 in 1862, determined the quantities both by experiments on animals 

 and on human beings. 



The results are — first, the expired air, at its own temper- 

 ature, is saturated with aqueous vapour ; secondly, the expired 

 air is less in volume than the inspired air to the extent of about 

 one-fortieth of the volume of the latter ; thirdly, the expired air 

 contains about 4 per cent, more carbonic acid and from 4 to 5 

 per cent, less oxygen than inspired air ; fourthly, the total daily 

 excretion of carbonic acid by an average man amounts to 800 

 grammes in weight, and 406 litres in bulk. This amount of 

 carbonic acid represents 2i8 - i grammes of carbon and 581*9 

 grammes of oxygen. The amount of oxygen, however, actually 

 consumed is about 700 grammes ; so. that nearly 120 grammes of 

 oxygen absorbed are not returned by the lungs, but disappear in 

 the body. It must be remembered, however, that carbonic acid 

 escapes by the skin and other channels. These figures may be 

 taken as averages, and are subject to wide variations depending 

 on nutritional changes. 



There is, however, another side to the problem of respiration 

 — namely, a consideration of the chemical changes involved in 

 the process. 



According to Lavoisier, respiration was really a slow combus- 

 tion of carbon and of hydrogen. The air supplied the oxygen, 

 and the blood the combustible ' materials. The great French 

 chemist, however, did not entirely commit himself to the opinion 

 that the combustion occurred only in the lungs. He says that a 

 portion of the carbonic acid may be formed immediately in the 

 lung, or in the blood-vessels throughout the body, by combina- 

 tion of the oxygen of the air with the carbon of the blood. 

 Lavoisier's opinions were understood correctly by only a few 

 of his contemporaries, and a notion prevailed that, according to 

 him, combustion occurred only in the lungs, and that the changes 

 in these organs were the main sources of animal heat. Such a 

 notion, however, was contrary to the opinion of the great mathe- 

 matician Lagrange, announced in 1791, a few years after the 

 first publication of Lavoisier's on respiration. Lagrange saw 

 that, if heat vere produced in the lungs alone, the temperature 

 of these organs might become so high as to destroy them ; and 

 he therefore supposed that the oxygen is simply dissolved in the 

 blood, and in that fluid combined with carbon and hydrogen, 

 forming carbonic acid and aqueous vapour, which were then set 

 free in the lungs. It will be observed that this opinion of 

 Lagrange in 1791 was practically the same as that stated by 

 Lavoisier in 1789. 



Now, if the production of carbonic acid in a given time de- 

 pended upon the amount of oxygen supplied in the same time, 

 these views of Lavoisier and Lagrange would be correct ; but 

 Spallanzani had shown that certain animals confined in an atmo- 

 sphere of nitrogen or of hydrogen exhaled carbonic acid to 

 almost as great an extent as if they had breathed air. He was 

 therefore obliged to say that carbonic acid previously existed in the 

 body, and that its appearance could not be accounted for by the 

 x Diagrams exhibited on wall. 



union of oxygen with the carbon of the. blood. Spallanzani 

 therefore thought that in the lung there was simply an exhalation 

 of carbonic acid and an absorption of oxygen These views 

 were supported by the experiments of W. Edwards, published 

 in 1824. Edwards showed that animals in an atmosphere of 

 hydrogen produced an amount of carbonic acid not to be 

 accounted for by any oxygen supposed to exist free in the body. 

 In 1830, Collard de Martigny performed many similar experi- 

 ments, and stated that carbonic acid was secreted in the 

 capillaries and excreted by the lungs. This opinion was 

 supported by Johannes Miiller, who repeated the experiments of 

 Spallanzani. 



It might thus be said that two theories of respiration were 

 before physiologists — the one, that combustion occurred in the 

 lungs or venous blood, furnishing carbonic acid and aqueous 

 vapour, which were exhaled by the lungs ; the other, that there 

 was no such combustion, but that oxygen was absorbed by the 

 lungs and carried to the tissues, whilst in these carbonic acid 

 was secreted, absorbed by the blood, carried to the lungs, and 

 there exhaled. Some writers, <oon after Lavoisier, misunder- 

 stood, as I have already stated, the opinions of that distinguished 

 man, and taught that in the lungs themselves there was a separa- 

 tion of carbon, which united immediately with the oxygen to 

 form carbonic acid. But this was really not Lavoisier's opinion ; 

 and we have to do, therefore, with two theories, which have 

 been well named — the theory of combustion, and the theory of 

 secretion. 



The difficulty felt by the older physiologists in accepting the 

 secretion theory was the absence of proof of the existence of free 

 oxygen and carbonic acid in the blood. This difficulty also met 

 those who rejected the notion of combustion occurring in the 

 lungs, and substituted for it the idea that it really occurred in the 

 blood throughout the body, because, if this were true, free gases 

 ought to be found in the blood. Consequently, so long as physio- 

 logists had no definite knowledge regarding gases in the blood, 

 the combustion theory, in the most limited sense, held its ground. 

 This theory, although fruitful of many ideas regarding respira- 

 tion and animal heat, was abandoned in consequence of the 

 evidence afforded by two lines of inquiry — namely, researches 

 regarding the gases of the blood, and researches as to the 

 relative temperature of the blood in the right and left cavities 

 of the heart. 



Let me first direct your attention to the gradual development 

 of our knowledge regarding the gases of the blood. The re- 

 markable change in the colour of the blood when it is exposed 

 to, or shaken up with, air was observed so long ago as in 1665 

 by Fracassati, and is also alluded to by Lower (1631-91), Mayow, 

 Cigna (1773), and Hewson (1774) ; but Priestley was the first to 

 show that the increased redness was due to the action of the 

 oxygen of the air, and that the blood became purple when agi- 

 tated with carbonic acid, hydrogen, and nitrogen. The presence 

 of gas in the blood was first observed about 1672 by Mayow. I 

 find in a paper of Leeuwenhoek (1632-1723), entitled "The 

 Author's Experiments and Observations respecting the Quantity 

 of Air contained in Water and other Fluids," published in 1674, 

 a description of a method devised by this ingenious man for de- 

 tecting the existence of air in certain fluids, and amongst them 

 in the blood. It consisted of a kind of syringe, by which he 

 was able to produce a partial vacuum. He then observed 

 bubbles of gas to escape, and he estimated, in the case of human 

 blood, that the air in the blood amounted to 1/1000 or 2/1000 

 part of the volume of the blood. He argues, from this interest- 

 ing observation, against one of the prevalent medical theories 

 of the time, that various diseases were caused by fermentations 

 in the blood. How, said he, was such a theory consistent with 

 the existence of so sma'l a quantity of gas? He made the 

 mistake, from the inefficiency of his apparatus, of stating that 

 blood, when it issues from the veins, contains no air. 



Gas was also obtained from the blood in 1799 by Sir Humphry 

 Davy, in 1814 by Vogel, in 1818 by Brand, in 1833 by Hoffmann, 

 and in 1835 by Stevons. On the other hand, John Davy, Berg- 

 mann, Johannes Miiller, Mitscherlich, Gmelin, and Tiedemann 

 failed in obtaining any gas. The first group of observers, either 

 by heating the blood, or by allowing it to flow into a vacuum, or 

 by passing through it a stream of hydrogen, obtained small 

 quantities of carbonic acid. Sir Humphry Davy was the first 

 to collect a small quantity of oxygen from the blood. John 

 Davy, by an erroneous method of investigation, was led, in 

 1828, to deny that the blood either absorbed oxygen or gave 

 off carbonic acid. He was shown to be wrong, in 1830, by 



