October 20, 1892] 



NATURE 



601 



It requires but a glance at the figures in this table to see that 

 the aerial differs markedly from the aquatic part of the respiration. 

 Even in the frog, in which the skin forms the only aquatic 

 respiratory organ, the tendency is marked. The law appears to 

 be unmistakably this, viz. that in combined aquitic and aerial 

 respiration, the aerial part is mainly for thesupply of oxygen and 

 the aquatic part largely for the excretion of carbon dioxide. 

 This law, which I stated in 1886, has been confirmed by the 

 repetition of old experiments and by many new ones made during 

 the present summer. It is also confirmed by the experiments 

 made on Lepidosteus in a different way by Dr. E. L. Mark, and 

 published in 1890. I therefore feel that this is the expression 

 of a general law in nature. 



From the standpoint of evolution we must suppose that all 

 forms originated from aquatic ancestors, ancestors whose only 

 source of oxygen was that dissolved in the water. As the water is 

 everywhere covered with the limitless supply of oxygen in the air, 

 there being 209 parts of oxygen in 1000 parts of air as contrasted 

 with the 6 parts of oxygen dissolved in 1000 parts of water, it is 

 not difficult to conceive that in the infinite years the animals 

 found by necessity and experience that the needed oxygen was 

 more abundant in the overlying air, and that some at least 

 would try more and more to make use of it. And as any thin 

 membrane with a plentiful blood supply may serve as a respir- 

 atory organ to supply the blood with oxygen, it is not impossible 

 to suppose that such a membrane, as in the throat, could 

 modify itself little by little with ever-increasing efficiency ; and 

 that a part might become especially folded to form a gill and 

 another might become sacular or lung-like to contain air. While 

 I am no believer in the purely mechanical physiology which 

 sees no need of more than physics and chemistry to render pos- 

 sible and explain all the phenomena of life, yet it is patent to 

 every one that, although vital energy is something above and 

 beyond the energies of physics and chemistry, still it makes use 

 of these ; and certainly dead matter forms the material from 

 virhich living is built. So given a living thing, it, in most cases, 

 moves along lines of least, rather than of greatest, resistance ; 

 therefore if practically a limitless supply of oxygen may be 

 obtained from the air and only a limited amount from the water, 

 if anything that might serve as a lung is present, most naturally 

 it (the animal) will take the oxygen from the air where it is in 

 greatest abundance and most easily obtained. On the other 

 hand, carbon dioxide is so soluble in water that practically a 

 limitless amount may be excaeted into it ; and as it is apparently 

 somewhat easier, other things being equal, for it to pass from 

 the liquid blood to the water than to the air, it seems likewise 

 natural that the gills should serve largely for the excretion of 

 the carbon dioxide into the water. This is the actual condition 

 before us in these, and I believe in all other cases, of mixed or 

 of combined aerial and aquatic respiration. And I believe, as 

 stated above, that it may be laid down as a fundamental law in 

 respiration that wherever both water and air are used with cor- 

 responding organs — gills for one and lungs for the other — that 

 the aerial part of the respiration is mainly for the supply of oxy- 

 gen, and the aquatic part largely for the getting rid of carbon 

 dioxide. 



It is not difficult to see in an actual case like that of the 

 Ganoid Fishes (Amia and Lepidosteus) the logical steps in its 

 evolution, by which this most favourable condition has been 

 reached. A condition rendering these fishes capable of living 

 in waters of almost all degrees of purity, and thus giving them a 

 great advantage in the struggle for existence. But what can be 

 said of the soft-shelled turtles, animals belonging to a group in 

 which purely aerial respiration i> almost exclusively the rule? 

 Standing alone, this might be exceedingly difficult or impossible 

 of explanation. The Batrachia (frogs, toads, salamanders, &c.) 

 all have gills in their early or larval stage, and most of them 

 develop in the water, and are in the beginning purely aquatic 

 animals. The adults must therefore, in most cases, repair to 

 the water at the spawning season and frequently in laying the 

 eggs they must remain under the water for considerable intervals. 

 Being under the water, and the need of oxygen becoming 

 pressing, there seems to be, by a sort of organic memory, a 

 revival of the knowledge of the way in which respiration was 

 accomplished, when, as larvae, their natural element was water, 

 and they take water into the mouth and throat. This may be 

 done by as highly a specialized and purely aerial form as the 

 little brown tree-frog {Hyla pickeringii) or the yellow spotted 

 salamander {Amblystoma ptinctatum). Another very interesting 

 form, the vermilion-spotted newt {Diemyctylus), after two or 



NO. I 199, VOL. 46] 



three years of purely aerial existence goes to the water on 

 reaching maturity and remains there the rest of its life, regularly 

 breathing both by its lungs and by taking water into its mouth 

 and threat. A still more striking example is given by Prof. 

 Cope. The young siren almost entirely loses its gills, and later 

 regains them, becoming again almost completely aquatic in its 

 habits as in the larval stage. 



With these examples, which may be seen by any one each 

 recurring year, is it impossible or difficult to conceive that in the 

 struggle lor existence the soft-shelled turtles found the scarcity 

 of food, the dangers and hardships on the land greater than 

 those in the water ? Or, remaining constantly in the water, and 

 advantageously submerged for most of the lime, it gradually 

 reacquired the power of making use of its pharyngeal membrane 

 for obtaining oxygen from the water and excreting carbon dioxide 

 into it as had its remote ancestors. And furiher,is it not intelligible 

 that with capacious lungs, which it can fill at intervals with air 

 containing so large z supply of oxygen that it, like the other 

 double or mixed breathers, should use its lungs to supply mo-<t 

 of the oxygen and its throat to get rid of much of the carbon 

 dioxide? 



Indeed it seems to me that if the evolution doctrine is a true 

 expression of the mode of creation, then development may be in 

 any direction that proves advantageous to an organism, even if 

 the development is a reacquirement of long discarded structures 

 and functions. 



In closing, may I be permitted to say to the older biologists — 

 to those familiar with the encouragements and inspirations that 

 come wiih original investigation, that I trust they will pardon 

 what to them is unnecessary personality or excess of detail in this 

 address, for the sake of the younger ones among us, to whom the 

 uphill road of research is less familiar. Judging from my own 

 experience in listening to similar addresses by my honoured pre- 

 decessors, it is helpful to know, when one is beginning, some- 

 thing of the "dead work," the difficulties and discouragements, 

 as well as the triumphs, in the advancement of science. 



MINES AND MINING AT THE CHICAGO 

 EXHIBITION. 



T'HE exhibition of objects relating to mines and mining at 

 the " World's Fair " promises to be one of exceptional 

 interest and importance. The following details about it were 

 given by Mr. George F. Kunz in a paper read before the recent 

 meeting of the American Association for the Advancement of 

 Science : — 



The building of mines and mining, which is entirely com- 

 pleted, is 700 feet long and 350 feet wide, at an elevation of 

 25 feet above the main floor. On both sides is a gallery 60 feet 

 wide, running the entire length of the building. Up to the 

 present time there have applied for space in this building 26 

 foreign Governments and 36 States, these exhibits to be sup- 

 plemented by other State and Government exhibits, such as 

 that of Sweden in the Swedish building, the East Indian in the 

 East Indian court, Illinois in their State building, &c. 



There will be a scientific collection of all the known elements, 

 and with them a complete collection of all the known alloys of 

 gold, silver, copper, zinc, tin, Ac, such as electrum, German 

 silver. Babbits metal, fusible metal, and the thousand and one 

 other, common and rare, used in the arts and industries. In the 

 name of the Lake Superior copper mines, Prof. Alex. Agassiz 

 has promised a complete exposition of ores, rocks, and pro- 

 cesses, illustrating the occurrence mining, metallurgy of copper. 

 There is now in preparation a coal collection to contain all 

 varieties of coal, from every known occurrence in the United 

 States. Petroleum will be shown as it never has been at any 

 exhibition. The subject of abrasives of all kinds will form a 

 special exhibit under the charge of Mr. T. Dunkin Paret, who 

 has devoted his entire life to this subject, and is now making a 

 special European trip to enlist the co-operation of foreign 

 manufacturers and investigators to supplement the American 

 exhibit. 



The De Beers Mining Company of South Africa, who own 

 and control moie than 95 per cent, of the entire diamond 

 output, will make first a full and comprehensive exposition of 

 diamond mining and the original blue stuff, a decomposed 

 peridotite, enclosing carbonaceous shale, the matrix of the 

 diamond, in great quantities. They will show it passing through 



