550 Physical Conditions of Inland Seas. 



Atlantic. In fact the almost asoic condition of the abyssal depths of the Mediter- 

 ranean, whilst its shallower portions teem -with life, shows that Edward Forbes's 

 doctrine (based on his researches in the _^gean) as to the limitation of animal life to 

 a depth of 300 fathoms, seems to be generally true of the Mediterranean, although 

 quite inapplicable to Oceanic basins. 



Whilst not abandoning the belief that the Turbidity of the bottom-water un- 

 favourably affects its suitableness as a residence for most marine animals, the Author 

 is now disposed to attribute more influence to the other condition wliich he suggested in 

 his Eeport for 1870 (p. 203), as likely to operate prejudicially to Animal life — namely, 

 the staff nation produced by the almost entire absence of vertical circulation. In the 

 great Oceanic system, if tbe doctrine previously advocated be correct, every drop of 

 water is, in its turn, brought to the surface, and exposed to the purifying influence of 

 prolonged exposure to Atmospheric air ; whereby a large proportion of its Carbonic 

 Acid and other products of the decomposition of Organic matter will be removed, 

 and Oxygen will be absorbed in their place. But from this movement the water of 

 the Mediterranean may be said to be virtually excluded. Now, as the Nile and the 

 Ehone, to say nothing of other rivers, are constantly bringing down a very large 

 quantity of Organic matter, tbe finer particles of which seem to be diffused through 

 tke whole mass of the water in the two basins, and to be slowly gravitating to their 

 bottom, it might be anticipated that in their gradual decomposition they would gene- 

 rate Carbonic Acid at the expense of the Oxygen dissolved in the water ; so that the 

 abyssal water, being separated from the atmosphere by an intervening stratum of 

 many hundred fathoms, and being never brought up to the surface, would come to be 

 unfit for the maintenance of animal life. 



Nowin ^^Porcupine Expedition of 1869 it was found that the pr«senceof a very large 

 proportion of Carbonic acid in the bottom-water of the Ocean was not incompatible with 

 the existence of Animal Life in great abundance. In fact, there \vas reason to believe 

 that there was a general relation of conformity between the proportion of Carbonic 

 acid and the amount of Animal life on the bottom as indicated by the dredge-results ; 

 the effect of the respiratory and other changes produced by the latter being to in- 

 crease the proportion of carbonic acid at the expense of the oxygen. Thus, whilst 

 the per-centage of Oxygen in surface-water averaged about 25 percent., and that of 

 Carbonic Acid averaged something less than 21 per cent., the Oxygen in bottom- 

 water did not average above 19-5 per cent., while the Carbonic acid had increased to 

 nearly 28, the per-centage of Nitrogen being reduced, at the same time, from 54 to 

 52'5. The per-centage of Carbonic acid in bottom-water often rose much higher than 

 this, being frequently between 30 and 40, and in one instance more than 48 ; but the 

 per-centage of Oxygen did not show a corresponding reduction, being never less than 

 16, while that of Nitrogen came down from 64 to 34-5. Thus it appeared that so 

 lonff as Oxygen was present in sufficient proportion, the increase of Carbonic acid to 

 nearly half the total amount of gases removable by boiling, did not exert any un- 

 favourable influence on Animal life ; from which it might be sui-mised that the Car- 

 bonic acid dissolved in water under great pressure is in a condition altogether difl'erent 

 from that of gaseous Carbonic acid, as regards its relation to Animal respiration. ^ 



In the Author's second visit to the Mediterranean, in the summer of 1871, each of 

 the samples of bottom-water taken in two deep Mediterranean soundings was boiled 

 until no more gas came over ; and the total quantity given ofl', which corresponded 

 very closely with the average obtained in former Expeditions, was divided in each case 

 into two parts, so that there were four specimens in all. The composition of these 

 specimens agreed very closely, the per-centages being approximately (for the Author 

 does not pretend to minute accuracy) as follows : — Oxygen, 5 ; Nitrogen, 35 ; and 

 Carbonic acid, CO. Thus it appeared that very nearly the whole available Oxygen 

 had been converted into Carbonic acid, so that while the proportion of Oxygen to 

 Carbonic acid was never, in the open sea, less than one-third, it was here no more 

 i\iaxi one-twelfth,— a, diiference fully adequate to account for the paucity of Animal 

 life on the deep bottom of the Mediterranean. 



That this condition does not extend to those moderate depths in which the water is 

 subjected to the disturbing action of winds, tides, and currents, may be fairly pre- 

 sumed; but whether it prevails through the whole stratum beneath 250 or 300 



1 It is by no means improbable tbat such sluggish animals as Mollusks and Ecbinoderms may 

 be able to bear a much larger proportion of Carbonic acid in the water they breathe, tlian Fishes 

 and Crustacea. Experimental inquiries upon this point, which might be readily carried out in 

 connexion with any large Aquarium, would give results of great Physiological interest. 



