400 



NATURE 



[August 23, 1888 



metres pressure ; and, as the average amount of haemoglobin in 

 blood is about 14 per cent., it follows that I '56 x 14 = 21 - 8 

 cubic centimetres of oxygen would be retained by 100 cubic 

 centimetres of blood. This agrees closely with the fact that 

 about 20 volumes of oxygen can be obtained from 100 

 volumes of blood. According to Pfliiger, arterial blood is satu- 

 rated with oxygen to the extent of nine-tenths, while Hiifner 

 gives the figure at fourteen-fifteenths. By shaking blood with 

 air, its oxygen contents can be increased to the extent of from 

 1 to 2 volumes per cent. 



These important researches, the results of which have been 

 amply corroborated, have given an explanation of the function 

 of the red blood corpuscles as regards respiration. The haemo- 

 globin of the venous blood in the pulmonary artery absorbs 

 oxygen, becoming oxyhaemoglobin. This is carried to the 

 tissues, where the oxygen is given up, the haemoglobin being 

 reduced. Thus, the colouring matter of the red blood corpuscles 

 is constantly engaged in conveying oxygen from the lungs to the 

 tissues. Probably the union of haemoglobin with oxygen, and 

 its separation from it, are examples of dissociation— that is, of a 

 ■chemical decomposition or synthesis, effected entirely by physical 

 conditions ; but data regarding this important question are still 

 wanting. If the union of oxygen with the colouring matter is 

 an example of oxidation, it must be attended with the evolution 

 of heat, but, so far as I know, this has not been measured. In 

 co-operation with my friend, Mr. J. T. Bottomley, I have recently 

 been able to detect, by means of a thermo-electric arrangement, 

 a rise of temperature on the formation of oxyhemoglobin. 

 We mean to prosecute our researches in this direction. If 

 heat were produced in considerable amount, the arterial blood 

 returned from the lungs to the left auricle would be hotter than 

 the blood brought to the right auricle by the veins. This, how- 

 ever, is not the case, as the blood on the right side of the heart 

 is decidedly warmer than the blood on the left — a fact usually 

 accounted for by the large influx of warm blood coming from the 

 liver. The heat-exchanges in the lungs are of a very complicated 

 kind. Thus, heat will be set free by the formation of oxyhemo- 

 globin ; but, on the other hand, it will be absorbed by the 

 escape of carbonic acid, and by the formation of aqueous vapour, 

 and a portion will be used in heating the air of respiration. 

 The fact that the blood in the left auricle is colder than that of 

 the right auricle is, therefore, the result of a complicated series 

 of heat-exchanges, not easy to follow. 



Our knowledge as to the state of the carbonic acid in the 

 blood is not so reliable. In the first place, it is certain that 

 almost the whole of the carbonic acid which may be obtained 

 exists in the plasma. Defibrinated blood gives up only a little 

 more carbonic acid than the same amount of serum of the same 

 blood. Blood serum gives up to the vacuum about 30 volumes 

 per cent, of carbonic acid ; but a small part — according to 

 Pfliiger, about 6 volumes per cent. — is given up only after 

 adding an organic or mineral acid. This smaller part is che- 

 mically bound, just as carbonic acid is united to carbonates, 

 from which it can be expelled only by a stronger organic or 

 mineral acid. The ash of serum yields about one-seventh of its 

 weight of sodium ; this is chiefly united to carbonic acid to form 

 carbonates, and a part of the carbonic acid of the blood is united 

 to those salts. It has been ascertained, however, that defibrin- 

 ated blood, or even serum containing a large number of blood 

 corpuscles, will yield a large amount of carbonic acid, even 

 without the addition of an acid. Thus, defibrinated blood will 

 will yield 40 volumes per cent, of carbonic acid — that is, 34 

 volumes which would be also given up by the serum of the same 

 blood (without an acid), and 6 volumes which would be yielded 

 after the addition of an acid. Something, therefore, exists in 

 defibrinated blood which acts like an acid in the sense of setting 

 free the 6 volumes of carbonic acid. Possibly the vacuum may 

 cause a partial decomposition of a portion of the haemoglobin, 

 and, as suggested by Hoppe-Seyler, acid substances may thus 

 be formed. 



But what is the condition of the remaining 30 volumes per 

 cent, of carbonic acid which are obtained by the vacuum alone? 

 A portion of this is probably simply absorbed by the serum ; this 

 part escapes in proportion to the decrease of pressure, and it may 

 be considered to be physically absorbed. A second part of this 

 carbonic acid must exist in chemical combination, as is indicated 

 by the fact that blood serum takes up far more carbonic acid 

 than is absorbed by pure water. On the other hand, this chemicai 

 combination is only a loose one, because it is readily dissolved by 

 the vacuum. There cah be no doubt that a part of this carbonic 

 acid is loosely bound to carbonate of soda, Na 2 C0 3 , in the serum, 



probably to acid carbonate of soda, NaIIC0 3 . This compound 

 exists only at a certain pressure. On a fall of pressure, it de- 

 composes into sodium carbonate and carbonic acid, the latter 

 becoming free. A third part of this carbonic acid is probably 

 loosely bound chemically to disodium phosphate, Na 2 HP0 4 , a 

 salt which also occurs in the blood serum. Fernet has shown 

 that it binds two molecules of carbonic acid to one molecule of 

 phosphoric acid. This salt occurs in considerable quantity only 

 in the blood of Carnivora and Omnivora, while in that of 

 Herbivora, such as in the ox and calf, only traces exist. It 

 cannot be supposed in the latter instances to hold much carbonic 

 acid in chemical combination. There must exist, therefore, 

 other chemical substances for the attachment of the carbonic 

 acid of the blood, and it has been suggested that a part may 

 be connected with the albumin of the plasma. 



According to Zuntz, the blood corpuscles themselves retain a 

 part of the carbonic acid, as the total blood is able to take up far 

 more carbonic acid out of a gaseous mixture rich in carbonic acid, 

 or consisting of pure carbonic acid, than can be absorbed by the 

 serum of the same quantity of blood. No compound, however, of 

 carbonic acid with the blood corpuscles is known. 



The nitrogen which is contained in the blood to the amount of 

 from I "8 to 2 volumes per cent., is probably simply absorbed, for 

 even water is able to absorb to 2 volumes per cent, of this gas. 



If we then "regard the blood as a respiratory medium having 

 gases in solution, we have next to consider what is known of the 

 breathing of the tissues themselves. Spallanzani was undoubtedly 

 the first to observe that animals of a comparatively simple type 

 used oxygen and gave up carbonic acid. But he went further, 

 and showed that various tissues and animal fluids, such as the 

 blood, the skin, and portions of other organs, acted in a similar 

 way. These observations were made before the beginning of the 

 present century, but they appear to have attracted little or no 

 attention until the researches of Georg Liebig on the respiration 

 of muscle, published in 1850. He showed that fresh muscular 

 tissue consumed oxygen and gave up carbonic acid. In 1856, 

 Matteucci made an important advance, by observing that mus- 

 cular contraction was attended by an increased consumption of 

 oxygen, and an increased elimination of carbonic acid. Since 

 then, Claude Bernard and Paul Bert, more especially the latter, 

 have made numerous observations regarding this matter. Paul 

 Bert found that muscular tissue has the greatest absorptive 

 power. Thus we arrive at the grand conclusion that the living 

 body is an aggregate of living particles, each of which breathes 

 in the respiratory medium passing from the blood. 



As the blood, containing oxygen united with the colouring 

 matter (haemoglobin), passes slowly through the capillaries, fluid 

 matter transudes through the walls of the vessels, and bathes the 

 surrounding tissues. The pressure or tension of the oxygen in 

 this fluid being greater than the tension of the oxygen in the 

 tissues themselves, in consequence of the oxygen becoming at 

 once a part of the living protoplasmic substance, oxygen is set 

 free from the haemoglobin, and is appropriated by the living 

 tissues, becoming part of their protoplasm. Whilst alive, or at 

 all events whilst actively discharging their functions, as in the 

 contraction of a muscle, or in those changes we term secretion in 

 a cell, the living protoplasm undergoes rapid decompositions, 

 leading to the formation of comparatively simple substances. 

 Amongst these is carbonic acid. As it has been ascertained that 

 the tension of the carbonic acid in the lymph is less than its 

 tension in venous blood, it is difficult at first sight to account for 

 the absorption of carbonic acid by venous blood ; but its tension 

 is higher than that of carbonic acid in arterial blood, and it must 

 be remembered that the lymph has had the opportunity, both in 

 the connective tissue and in the lymphatic vessels, of modifying 

 its tension by close contact with arterial blood. Strassburg 

 fixes the tension of the carbonic acid intthe tissues as equal to 

 45 mm. of mercury, while that of the venous blood is only 

 41 mm. We may assume that as the carbonic acid is set free, it 

 is absorbed by the blood, uniting loosely with the carbonates and 

 phosphates of that fluid, thus converting it from the arterial into 

 the venous condition. This constitutes respiration of tissue. 



In connection with the respiration of tissue, as determined by 

 the analysis of the blood gases and of the gases of respiration, 

 there arises the interesting question of the ratio between the 

 amount of oxygen absorbed and the amount of carbonic acid pro- 

 duced, and very striking contrasts among animals have thus been 

 determined. Thus in Herbivora the ratio of the oxygen absorbed 

 to the carbonic acid produced, or the respiratory quotient, as it 

 is termed by Pfliiger, ^? amounts to from o* to 10, while in 



