August 23, 1888] ' 



NATURE 



401 



Carnivore it is from 075 to o'8. Omnivora, of which man may 



be taken as the example, come between - = o'87. Thequo- 





 tient is greater in proportion to the amount of carbohydrate in the 

 diet, whether the animals are Carnivora, Herbivora, or Omnivora. 

 The respiratory quotient becomes the same, about 075, in starv- 

 ing animals, a proof that the oxidations are kept up at the cost of 

 the body itself, or, in other words, the starving animal is car- 

 nivorous. The intensity of respiration in different animals is 

 well shown in the following table, in which the amount of 

 oxygen used is given per kilogramme of body-weight per hour 

 (Dr. Immanuel Munk, " Physiologie des Menschen und der 

 Siingethiere," 1888, p. 82J. 



Respiratory 

 Animal. O in grammes. ^O.?"'' 



o"' 

 Cat 1007 077 



D °g 1*183 075 



Rabbit 0-918 o'Q2 



Hen 1 -300 0-93 



Small singing birds ... 11-360 078 



Frog 0-084 063 



Cockchafer ... ... 1 '019 ... ... -o'8i 



Man 0-417 0-78 



Horse 0563 0*97 



Ox 0*552 ... ... 0-98 



Sheep ... .. 0-490 ... ... 0-98 



Smaller animals therefore have, as a rule, a greater intensity of 

 respiration than larger ones. In small singing birds the intensity 

 is very remarkable, and it will be seen that they require ten times 

 as much oxygen as a hen. On the other hand, the intensity is 

 low in cold-blooded animals. Thus a frog requires 135 times 

 less oxygen than a small singing bird. The need of oxygen is 

 therefore very different in different animals. Thus a guinea-pig 

 soon dies with convulsions in a space containing a small amount 

 of oxygen, while a frog will remain alive for many hours in a space 

 quite free of oxygen. It is well kn >wn that fishes and aquatic 

 animals generally require only a small amount of oxygen, and 

 this is in consonance with the fact that sea-water contains only 

 small quantities of this gas. Thus, according to the elaborate 

 researches of my friend, Prof. Dittmar, on the gases of the sea- 

 water brought home by the Cha/Ienger Expedition, collected in 

 many parts of the great oceans, and from varying depths : — " The 

 ocean can contain nowhere more than 15 '6 c.c. of nitrogen, or 

 more than 8"i8 c.c. oxygen per litre ; and the nitrogen will never 

 fall below 8-55 c.c. We cannot make a similar assertion in re- 

 gard to the oxygen, because its theoretical minimum of 4-30 c.c 

 per litre is liable to further diminution by processes of life and 

 putrefaction and processes of oxidation " (Dittmar, Proceedings 

 of Phil. Soc. of Glasgow, vol. xvi. p. 61). As a matter of fact, 

 a sample of water from a depth of 2875 fathoms gave only 

 o*6 c.c. per litre of oxygen, while one from a depth of 1500 

 fathoms gave 2-04 c.c. per litre. Taking I5°C. as an average 

 temperature, one litre of sea-water would contain only 5-31 c.c. 

 of dissolved oxygen— that is, about 0-5 c.c. in 100 c.c. Contrast 

 this with arterial blood, which contains 20 c.c. of oxygen in 

 100 c.c. of blood, or there are about forty times as much oxygen 

 in arterial blood as in sea- water. At great depths the quantity 

 of oxygen is very much less, and yet many forms of life exist at 

 these great depths. Fishes have been dredged from a depth of 

 2750 fathoms, where the amount of oxygen was probably not 

 so much as o'o6 c.c. per 100 c.c, or 300 times less than that 

 of arterial blood. Making allowance for the Smaller quantity of 

 oxygen in the blood of a fish than that of a mammal, it will still 

 be evident that the blood of the fish must contain much more 

 oxygen than exists in the same volume of sea- water. No doubt 

 we must remember that the water is constantly renewed, and that 

 the oxygen in it is in the state of solution, or, in other words, 

 in a liquid state. But the question remains, where do these deep- 

 sea creatures obtain the oxygen ? Probably by a method of 

 storage. Biot has found in. the swimming-bladder of such fishes 

 70 volumes per cent, of pure oxygen, a gas in which a glowing 

 splinter of wood is relit. This oxygen probably oxygenates the 

 blood of the fish when it plunges into the dark and almost airless 

 depths of the ocean. 



Aquatic breathers, however, if they live in a medium contain- 

 ing little oxygen, have the advantage that they are not troubled 

 with free carbonic acid. One of the most striking facts discovered 

 by the Challenger chemists is that sea-water contains no free 



carbonic acid, except in some situations where the gas is given 

 oli by volcanic action from the crust of the earth forming the 

 sea-bed. In ordinary sea-water there is no free carbonic acid, 

 because any carbonic acid formed is at once absorbed by the 

 excess of alkaline base present. Thus the fish breathes on the 

 principle of Fleuss's diving apparatus, in which the carbonic acid 

 formed is absorbed by an alkaline solution. There is nothing 

 new under the sun. The fish obtains the oxygen from the sea- 

 water, no doubt, by the chemical affinity of its haemoglobin, 

 which snatches every molecule of oxygen it may meet with, 

 while it gets rid of its carbonic acid easily, because there is not 

 only no tension of carbonic acid in the sea-water to prevent its 

 escape, but there is always enough of base in the sea-water to 

 seize hold of the carbonic acid the moment it is formed. If we 

 could get rid of the carbonic acid of the air of expiration as 

 easily, we could live in an atmosphere containing a much smaller 

 percentage of oxygen. 



I have now placed before you the generally accepted doctrines 

 regarding the chemical and physical problems of respiration. 

 But one has only to examine them closely to find that there are 

 still many difficulties in the way of a satisfactory explanation of 

 the function. For example, is the union of haemoglobin with 

 oxygen a chemical or a physical process ? If oxyhemoglobin is 

 a chemical substance, how can the oxygen be so readily removed 

 by means of the air-pump ? On the other hand, if it is a 

 physical combination, why is the oxygen not absorbed according 

 to the law of pressure ? It is important to note that, as a matter 

 of fact, haemoglobin absorbs a quantity of oxygen nearly constant 

 for ordinary temperatures, whatever may be the amount of oxy- 

 gen present in the mixture of gases to which it is exposed. This 

 is true so long as the amount of oxygen does not fall below a 

 certain minimum, and it clearly points to the union of the haemo- 

 globin with the oxygen being a chemical union. Suppose we 

 diminish the amount of oxygen in the air breathed, the partial 

 pressure of the gas is of course also diminished, but it is evident 

 that we might diminish the total pressure instead of diminishing 

 the amount of oxygen. To avoid difficulties in respiration, when 

 one is obliged to breathe an air deficient in oxygen, we ought to 

 increase the pressure at which the air is breathed ; and, on the 

 other hand, to avoid danger in breathing air under a low 

 pressure, we ought theoretically to increase the richness of the 

 air in oxygen. Thus, with a pressure of 760 mm. the air should 

 contain, as it normally does, 21 per cent, of oxygen, while with 

 a pressure of 340 mm. it should contain 46 per cent., and with 

 a pressure of 250 mm. it should contain as much as 63 per cent. 

 On this basis a pressure of 5 atmospheres should be associated 

 with an atmosphere containing about 3 per cent, of oxygen. By 

 increasing the pressure, we increase the quantity of oxygen by 

 weight in a given volume. 



The explanation is that in all of these cases the partial pressure 

 of the oxygen is nearly the same — that is, not far from 157 mm. 

 of mercury, and the general law is that for all kinds of breathing 

 the pressure of the oxygen should be nearly that of the oxygen 

 in ordinary atmospheric air. Whilst the absorption of oxygen 

 by the haemoglobin has nothing directly to do with the pressure, 

 it is striking that any atmosphere contains enough oxygen by 

 weight for the haemoglobin in the blood, when the partial 

 pressure of the oxygen is near 157 mm. On each side of this 

 median line life can be supported with considerable differences 

 of pressure. Thus the pressure may be gradually reduced until 

 the point of the dissociation of oxyhemoglobin is reached — that 

 is to say, down to about T V of an atmosphere. On the other 

 hand, animals may breathe an atmosphere containing two or 

 three times the normal amount of oxygen without appearing to 

 be affected. This was first noticed by Regnault and Reiset, and 

 the observation has been much extended by Paul Bert. The 

 latter distinguished physiologist found that an increase even up 

 to 8 or 10 atmospheres did not produce any apparent effect, 

 but on reaching the enormous pressure of 20 atmospheres, death, 

 with severe tetanic convulsions, was the result. He also showed 

 that the additional increment of oxygen absorbed by the blood 

 under the influence of each atmosphere of added pressure was 

 very small. Thus, with a pressure of I atmosphere the amount 

 of oxygen absorbed by the blood was about 20 per cent, by 

 volume, a pressure of 2 atmospheres caused an increase of 

 only o'9 per cent., of 3 atmospheres 07 per cent,, of 4 atmo- 

 spheres o"6 per cent., of 5 atmospheres 0-5 per cent., of 6 

 atmospheres o"2 per cent., of 7 atmospheres o"2 per cent., of 8 

 atmospheres o-i per cent., of 9 atmospheres o - i percent., and 

 of 10 atmospheres o'i per cent. Thus from 1 atmosphere to 10 

 atmospheres the increase was only to the extent of 3-4 per cent., 



