Aristotle On Youth and Old Age,On Life and Death,On Breathing-Part 7 & 8

7
A few of the previous physical philosophers have spoken ofrespiration. The reason, however, why it exists in animals they haveeither not declared or, when they have, their statements are notcorrect and show a comparative lack of acquaintance with the facts.Moreover they assert that all animals respire-which is untrue. Hencethese points must first claim our attention, in order that we maynot be thought to make unsubstantiated charges against authors nolonger alive.First then, it is evident that all animals with lungs breathe, butin some cases breathing animals have a bloodless and spongy lung,and then there is less need for respiration. These animals canremain under water for a time, which relatively to their bodilystrength, is considerable. All oviparous animals, e.g. the frog-tribe,have a spongy lung. Also hemydes and tortoises can remain for a longtime immersed in water; for their lung, containing little blood, hasnot much heat. Hence, when once it is inflated, it itself, by means ofits motion, produces a cooling effect and enables the animal to remainimmersed for a long time. Suffocation, however, always ensues if theanimal is forced to hold its breath for too long a time, for none ofthis class take in water in the way fishes do. On the other hand,animals which have the lung charged with blood have greater need ofrespiration on account of the amount of their heat, while none atall of the others which do not possess lungs breathe.

8
Democritus of Abdera and certain others who have treated ofrespiration, while saying nothing definite about the lungless animals,nevertheless seem to speak as if all breathed. But Anaxagoras andDiogenes both maintain that all breathe, and state the manner in whichfishes and oysters respire. Anaxagoras says that when fishes dischargewater through their gills, air is formed in the mouth, for there canbe no vacuum, and that it is by drawing in this that they respire.Diogenes' statement is that, when they discharge water through theirgills, they suck the air out of the water surrounding the mouth bymeans of the vacuum formed in the mouth, for he believes there isair in the water.But these theories are untenable. Firstly, they state only what isthe common element in both operations and so leave out the half of thematter. For what goes by the name of respiration consists, on theone hand, of inhalation, and, on the other, of the exhalation ofbreath; but, about the latter they say nothing, nor do they describehow such animals emit their breath. Indeed, explanation is for themimpossible for, when the creatures respire, they must dischargetheir breath by the same passage as that by which they draw it in, andthis must happen in alternation. Hence, as a result, they must takethe water into their mouth at the same time as they breathe out. Butthe air and the water must meet and obstruct each other. Further, whenthey discharge the water they must emit their breath by the mouth orthe gills, and the result will be that they will breathe in andbreathe out at the same time, for it is at that moment thatrespiration is said to occur. But it is impossible that they should doboth at the same time. Hence, if respiring creatures must bothexhale and inhale the air, and if none of these animals can breatheout, evidently none can respire at all.