6oo 



NATURE 



[October 20, 1892 



direct with the insects, however, for the oxygen and carbon 

 dioxide mast pass through the membranous wall of the air-tube 

 before reachiiii» or leaving the living substance. 



In the next and tinal step, the step taken by the highest 

 forms, the living material is massed, giving rise not only to 

 animals of mo lerate size, but to the huge creatures that swarm 

 in the seas or walk the earth, liki the elephant. With all of 

 these the step in the differentiation of the respiratory mechanism 

 consists in the great perfection of lungs or gills, and in the 

 addition of a complicated circulatory system with a respiratory 

 blood, one of the main purposes being, as the name indicates, 

 to subserve in respiration by carrying to each individual cell in 

 the most remote and hidden part of the body the vital air, and 

 in the same journey removing the poisonous carbon dioxide. 



This has been called Indirect Respiration, because the living 

 matter of the body does not take its oxygen directly either from 

 air or water, but is supplied by a middleman, so to speak. 



The complicated movements by which water is forced over the 

 gills, or by which the lungs are filled and emptied, and the great 

 currents of blood are maintained — that is, the striking and easily 

 observed phenomena of respiration are thus seen to be only 

 superficial and accessory, only serve as agents by which the real 

 and the essential processes, that go on in silence and obscurity, 

 are made possible. 



So far I have attempted to give a brief resume of the views 

 on respiration that have been slowly and laboriously evolved by 

 many generations of physioJogists, each adding some new fact 

 or correcting some misconception ; and I trust that this brief 

 sketch has recalled to your minds the salient facts in our know- 

 ledge of respiration, and that it will give a just perspective, and 

 enable me, if I may be permitted, to briefly describe what I 

 believe to be my own contribution to the ever-accumulating 

 knowledge of this subject. 



In 1876-77, Prof. Wilder, who may be said to have inherited 

 his interest in the ganoid fishes directly from his friend and 

 teacher, Agassiz, who first recognized and named the group, 

 was investigating the respiration of the forms Amia and 

 Lepidosteus, common in the great lakes and the western rivers. 

 As his assistant it was my privilege to aid in the researches, and 

 to acquire the spirit and methods as in no other way is it so 

 readily possible, by following out, from the beginning to its 

 close, of an investigation carried on by a master. The results 

 of that investigation were reported to this section in 1877, and 

 formed a part of the proceedings for that year. From that time 

 ^ till the present the problems of respiration in the living world 



have had an ever increasing fascination for me, and no oppor- 

 tunity has been lost to investigate the subject. The interest 

 was greatly increased by the discovery that a reptile — the soft- 

 shelled turtle — did not conform to the generalizations in all the 

 treatises and compendiums of zoology, which state with the 

 greatest definiteness that all reptiles, without exception, are 

 purely air-breathing, and throughout their whole life obtain 

 their oxygen from the air and never from the water. The 

 American soft-shelled turtles, at least, do not conform to this 

 generalization, but on the contrary, naturally and regularly 

 breathe water like a fish, as well as air like an ordinary reptile, 

 bird, or mammal. 



In carrying on the investigation of the respiration of the 

 turtle, there appeared for solution the general problem, which, 

 briefly slated, is as follows : In case an animal breathes both air 

 and water, or more accurately, has both an aerial and an 

 aquatic respiration, like the ganoid fishes, Amia and Lepidosteus, 

 like the soft-shelled turtles, the tadpoles, and many other 

 forms, what part of the respiratory process is subserved by the 

 aqueous and what by the aerial part of the respiration ? So 

 far as I am aware this problem had not been previously con- 

 sidered. It was apparently assumed that there were in these 

 fortunate animals two independent mechanisms, both doing 

 precisely the same kind of work — that is, each serving to supply 

 the blood with oxygen and to relieve it of carbon dioxide, as 

 though the other was absent. That was a natural inference, for 

 with many forms the respiration is wholly aquatic, all the oxygen 

 employed being taken from the water, and all the carbon 

 dioxide excreted into it. On the other hand, in the ex- 

 clusively air-breathing animals, as birds and mammals, the 

 res iration is exclusively aerial. 



This natural supposition was followed in the first investigations 

 on the respiration of the soft-shelled turtles, and while it was 

 proved with incontestable certainty that they take oxygen from 

 the water like an ordinary fish — that is, have a true aquatic 



respiration, in addition to their aerial respiration— there was 

 altogether too much carbon dioxide in the water to be accoumed 

 for by the oxygen taken from it. Furthermore, upon analyzing 

 the air from the lungs of a turtle that had been submerged some 

 time the oxygen had nearly all disappeared, and but very little 

 carbon dioxide was found in its place, while, as compared with 

 human respiration, for example, a quantity of carbon dioxide 

 nearly as great as that of the oxygen which had disappeared 

 should have been returned to the lungs. Likewise in Professor 

 Wilder's experiments with Amia, to use his own words : 

 *' Rather more than one per cent, of carbon dioxide is found in 



! the normal breath of the Amia, but much more of the oxygen 

 has disappeared than can be accounted for by the amount of 

 carbon dioxide." Everything thus appeared anomalous in this 

 mixed respiration, and instead of a clear, consistent, and in- 



I telligible understanding of it, there seemed only confusion and 

 ambiguity. Truly these seemed like " bad experiments." 



I It became perfectly evident that the first step necessary in 



' clearing the obscurity was to separate completely the two 



j respiratory processes, to see exactly the contribution of each 

 mechanism to the total respiration. But this was no easy thing 



[ to do. In the first place, the animal must be confined in a 

 sor"ewhat narrow space in order that air and water, which are 

 known to have been affected by its respiration, may be tested to 



. show the changes produced in it by the respiratory process ; in 

 the second place, the water has so great a dissolving power 

 upon carbon dioxide that even if it were breathed out into the 



! air it would be liable to be absorbed by the water. Then some 

 means must be devised to prevent the escape of the gases from 

 the water as their tension becomes changed ; and, finally, the 

 animal in the water must be able to reach the air. A diaphragm 

 must be devised which would prevent the passage of gases 

 between the air and the water, and at the same time offer no 

 hindrance to the animal in projecting its head above the water. 

 As a liquid diaphragm must be used, it occurred to me that 

 some oil would serve the purpose, but the oil must be of peculiar 

 nature. It must not allow any gases to pass from air to water, 

 or the reverse ; it must not be in the least harmful or irritating 

 to the animal under experimentation, and, finally, it must itself 

 add nothing to either air or water. Olive oil was thought of, 

 and later the liquid paraffins. The latter were found practically 

 impervious to oxygen and fulfilled all the other requirements, 

 but unfortunately they absorb a considerable quantity of carbon 

 dioxide. Pure olive oil was finally settled upon as furnishing 

 the nearest approximation to the perfect diaphragm sought.^ 



The composition of the air being known, and a careful de- 

 termination of the dissolved gases in the water having been 

 made, the animal was introduced into the jar and the water 

 covered with a layer of olive oil from ten to fifteen millimetres 

 thick. The top of the jar was then vaselined, and a piece of 

 plate-glass pressed down upon it, thus sealing it hermetically. 

 Two tubes penetrate this plate-glass cover, one connecting with 

 the overlying air-chamber and the other extending into the water 

 nearly to the bottom of the jar. As the water and air are 

 limited in quantity, the shorter the time in which the animal 

 remained in the jar the more nearly normal would be the 

 respiratory changes, the experiment was continued on'y so long 

 — one or two hours — as was found necessary to produce sufficient 

 change in the air and the dissolved gases of the water to render 

 the analyses unmistakable. 



Proceeding with the method just described, the results given 

 in the following table were obtained : — 



Table of Mixed Respiration, showing the number of cubic centi- 

 metres of oxygen removed from air anduater, and the amount 

 of carbon dioxide added to the air and the water. 



Oxygen Carbon Dioxide 

 from from 



Ganoid Fish {Amia calva) . . 65 

 Tadpoles {Larval Batrachia) . 70 

 Soft-shelled Turtle {Amyda mutica) 31 

 '2>\s\\Yxoz{Rana catesbiana) . 183 

 Note. — The cxygen from both the water and the air, and the carbon dioxide 

 in the air, were determined with exactness in all the e.\perinients ; but 

 owing to the failure of son;e steps in the titration for the carbcn dioxide in 

 the water, the figures given for the Amia and the sijfi-:rhelkd turtle are the 

 calculated results, as.'-uming that the re^piratory quotient is one, as that is 

 the relation f und by ai.alysis in ihe other cases. 



' See Wm. Thorner on the use of olive oil (or the prevention of the ab- 

 sorption of carbon dioxide. Repertonum der analytitchen Chemie. 1885, 

 i PP- 15-17- 



NO. r 199, VOL. 46] 



