356 



NA TURE 



[August io, 1905 



and a half times greater than the land surface. He would 

 discover that there are animals that live in air, others in 

 water, and again others on land. Our visitor would find 

 out that the respirable media are two — water and air — 

 and that there are 210 parts of free oxygen in a litre of 

 air, while there are only 3-10 dissolved in a litre of 

 water. 



Had Voltaire's friend paid us another visit during the 

 present century, we should be able to tell him that the 

 water of the Thames above London contains 7-40 c.c. of 

 O per litre ; at Woolwich only 0-25, the decrease being 

 due to the pollution of the river. Putting it broadly, 

 water contains only 3-10 parts per litre, while air contains 

 210. \\'ater-breathers under good conditions have twenty 

 times less O than air-breathers. It is as if air-breathers 

 on land had the percentage of O, reduced to i. 



He would also be told that carbon dioxide — CO. — is 

 also remarkably soluble in water, and readily combines 

 with certain bases present in water ; thus water forms an 

 admirable medium into which an animal may discharge 

 its effete and poisonous irrespirable CO.. 



He would also be told that our blood contains 60 volumes 

 per cent, of gases, and that there is more O and less CO. 

 in arterial blood than in venous blood. 



Perhaps the name of Sir H. Davy might be whispered 

 to him, for he was one of the first to detect the presence 

 of gases O and CO. in blood. 



In story, one has heard of the " Quest of the Holy 

 Grail." 1 have even listened with rapt attention to an 

 entrancing lecture on the " Quest of the Ideal." For the 

 cell, the quest is the "quest of o.\ygen, " and it is not 

 happy until it gets it. 



AVe speak of a distinction between air-breathers and 

 water-breathers. If, however, we push the matter to its 

 ultimate issue, we find that all our tissues — and equally 

 those of plants — live in a watery medium ; in us the fluid 

 lymph which exudes from our capillary blood-vessels, and 

 in plants in the sap. Thus we come upon what at first 

 seems a paradox, but is not so ; all our cells not only live 

 in water, but they live in running water. They are bathed 

 everywhere by tfie lymph which is the real nutrient fluid 

 for our cells. Thus, in its final form, all respiration is 

 actually aquatic. The process of internal respiration, 

 besides other conditions, requires the presence of a certain 

 amount of water. In fact, all vital phenomena require 

 the presence of water. 



The unity and identity of the process in animal and 

 vegetable cells, as the theatre of combustion, is the striking 

 fact. The means by w-hich the necessary oxygen is 

 brought to the cells is as varied as the forms of animated 

 organisms themselves. This function exists for the cells, 

 and not the cells for the function. 



If the mountain will not go to Mohammed, Mohammed 

 rnust go to the mountain. There are, at least, two prin- 

 ciples on which animal cells obtain oxygen. 



The air or water containing air is carried to the cells. 

 This is the principle adopted in the lower invertebrates, as 

 in sponges and with regard to certain air-breathers such 

 as insects. 



The other principle is this, that an intermediary carries 

 the respiratory o.\ygen from some more or less central 

 localised or diffu.se surface to the cells. This intermediary 

 is the blood — an internal medium of e.xchange. The fluid 

 part of the blood may carry the oxygen supply and remove 

 the carbonic dioxide waste. This is the case in many of 

 the invertebrates, and it reaches its highest developnient 

 in the vertebrates. Hence in them the circulating and 

 respiratory systems reach their fullest development. 



In most invertebrates the fluid part of the blood contains 

 the nutritive substances and also the oxygen and carbonic 

 acid. In the vertebrates, the haemoglobin of the red blood 

 corpuscles carries the oxygen from the gills or lungs to the 

 tissues, whilst the CO, is contained in and carried chiefly 

 by the blood plasma from the tissues to the gills or lungs. 



It is singular that in the cephalopods, such as the squid 

 and cuttle-fish, the blood is bluish in tint ; and this is 

 due to the presence in the plasma of a respiratory pig- 

 nient called ha-mocyanin. This bodv has a composition 

 like that of haemoglobin, but copper 'is substituted for the 

 iron of the h.-emoglobin. Copper also exists in organic 

 NO. 1867, VOL. 72] 



combination in the red part of the feathers of the plantain- 

 eater or turaco. 



The real aristocracy with genuine blue blood are the 

 crab, lobsters, squids, and cuttle-fishes. 



Perhaps one of the most striking ways of dissociating 

 this accessory mechanism from the activity of the cell 

 itself is bv the use of a poison. When a person is 

 poisoned by coal gas, what happens? The coal gas con- 

 tains carbon mono.xide. This gas does nbt poison inverte- 

 brate animals or plants. .Still it kills vertebrate animals. 

 Why? It does not kill by acting on the living cells, only 

 by depriving them of oxygen and asphy.xiating them. It 

 combines with the respiratory pigment haemoglobin. 

 Chloroform, ether, and similar drugs destroy the actual life 

 of the cell elements by destroying their irritability. 



In 1771, Priestley found that air vitiated by combustion 

 of a candle, or by the breathing of animals — such as mice 

 — could be made pure or respirable again by the action of 

 green plants. 



L'nder certain conditions, however, Priestley found that 

 plants gave off carbonic acid, and the air did not support 

 combustion or animal life. He regarded these as " bad 

 experiments," and he selected what he was pleased to 

 regard as " good experiments," i.e. those in which the 

 air, rendered impure by the respiration of animals, was 

 rendered respirable by the action of green plants. 



In 1779 John Ingen-Housz published his " Experiments 

 on Vegetables, discovering their great power of purifying 

 the common air in sunshine, and of injuring it in the shade 

 and at night." 



He confirmed Priestley's observations that green plants 

 thrive in putrid air. and that vegetables could convert air 

 fouled by burning of a candle, and restore it again to its 

 former purity and fitness for supporting flame, and for the 

 respiration of animals — or, as he puts it, " plants correct 

 bad air." 



In 1787 Ingen-Housz, an English physician at the 

 Austrian court, found that only in daylight did green plants 

 give off oxygen. In darkness, or where there was little 

 light, they behaved like animals so far as exchange of 

 gases is concerned, i.e. they used up oxygen and exhaled 

 carbonic acid. He found also that all roots, when left out 

 of the ground, yielded by day and by night foul air, i.e. 

 carbonic acid. 



In the same year, 1804 — the year of Priestley's death — 

 Nicolas Theodore de Saussure, a Swiss naturalist and 

 chemist, published his " Recherches Chimiques sur la 

 A'^g^tation " (Paris, 1804), a veritable encvclopa;dia of 

 experiments of the effects of air on flowers, fruits, plants, 

 and vegetation generally, and on the effects of these on 

 atmospheric acid. 



It is an old adage— the exception proves the rule. The 

 exception " probes " the rule as the surgeon's probe probes 

 a wound. The tactus eruditus of the surgeon, bv his 

 probe — indeed an elongated tactile sense — enables him to 

 discover the presence or absence of a body in a wound. 

 Had Priestley used the probe of a bad experiment, he in 

 all probability would have anticipated the discoverv of 

 Ingen-Housz. 



.Some of you, no doubt, recollect the word^ of Cold- 

 smith's famous description of his own bedroom and of the 

 furniture of the inn — 



" The house where nut-brown draughts inspired." 

 .\nd how his imagination stooped to trace the storv of — 

 " The chest that contrived a double debt to ray, 

 .4 bed by night, a chest of drawers by day." 

 As to himself he tells us how — 



" A night-cap decked his brows instead of bay, 

 A cip by night— a stocking all the day." 



Green plants contrive a double debt to pav ; thev give off 

 oxygen by day, and at night exhale CO.. 



How do the vast number of plants, "the microbes, the 

 bacteria without chlorophyll get oxygen? Most of them 

 get it as we get it. Some, however, cannot live in pure 

 oxygen and are anferobic, such as the micro-organisms 

 that cause tetanus, malignant oedema, and those that set 

 up butyric acid fermentation. 



Pushing the matter still further, it is extremely probable 

 that the oxidation processes in our tissues are largely due 

 to the presence of o.xydases. 



