426 



NA TURE 



\August 28, 1884 



received but little attention from professed physiologists. No 

 physiologist has, as far as I am aware, as yet set forth com- 

 prehensively and dwelt upon the numerous difficulties which are 

 encountered when the attempt is made to comprehend the mode 

 in which the ordinary physiological processes of Vertebrata and 

 other animals are carried on under the peculiar physical con- 

 ditions which exist at great depths. 



Whilst I was on the Chall nrer voyage, absorbed principally 

 in the zoological discoveries daily resulting from the dredging 

 operations, I received a letter from my revered teacher, Prof. 

 Ludwig, of Leipzig, which brought deep-sea phenomena before 

 me in a very different light. The Professor naturally regarded 

 deep-sea questions mainly from a physiological point of view, 

 and asked a series of most suggestive questions bearing on it. I 

 am much indebted to him for this and recent letters on the same 

 subject. One of the first questions he asked was, naturally, as 

 to the amount of oxygen present in deep-sea water. A know- 

 ledge of the conditions under which gases occur in a state of 

 absorption in the ocean-waters is of primary importance to the 

 physiologist. With regard to this subject, most valuable in- 

 formation is contained in the report by the distinguished chemist, 

 Prof. Dittmar, on "Researches into the Composition of the 

 Ocean- Water collected by H.M.S. Challenger," which has ap- 

 peared during the present year, and which embody Mr. I. Y. 

 Buchanan's results. 1 It appears from his results that, contrary 

 to what was before suspected, the presence of free carbonic acid 

 in sea-water is an exception. What carbonic acid is present 

 occurs as a bicarbonate, in general more or less incompletely 

 saturated. In surface-waters the proportion of carbonic acid 

 increases when the temperature falls, and vice versa. Deep-sea 

 water doe; not contain an abnormal proportion of loose or free 

 carbonic acid. 



Hence, with regard to Mr. John Murray's interesting dis- 

 covery that after certain depths are reached Pceropod shells are 

 dissolved and disappear from the sea-bottom, and at certain 

 further depths Globigerina shells suffer the same fate, Prof. 

 Dittmar holds the opinion that the solution is not due to the 

 presence of free acid, but to the solvent action of the sea-water 

 itself, which will, even when alkaline, take up additional car- 

 bonate of lime if sufficient time be given. Thus the amount of 

 carbonic acid normally present throughout the ocean cannot be 

 inimical to life ; but, according to the Professor, there must be 

 in the depths of the ocean numerous bodies of richly carbonated 

 water, for he regards the principal supply of carbonic acid to the 

 sea-water as derived from volcanic springs and discharges issuing 

 from the ocean-bed, the quantity derived from the decay of 

 marine plants and animals being insignificant in comparison with 

 this. Possibly the Challenger, when it dredged from deep water 

 off the Azores immense quantities of dead and blackened coral, 

 encountered an area which had thus been visited by a carbonic 

 acid discharge. 



With regard to the absorbed oxygen and nitrogen, the theo- 

 retical maximum quantity of oxygen absorbed at normal surface- 

 pressure by a litre of sea-water should range, according to 

 Prof. Dittmar's experiments and calculations, from 8'iS c.c. 

 in cold regions at 0° C. to 4-50 c.c. in the tropics, with a tem- 

 perature of 30° C. The result experimentally obtained from 

 samples of surface-water collected durinj the voyage differ con- 

 siderably in detail from the calculated estimates, from various 

 causes explained, and especially because of the reduction of the 

 amount of oxygen by oxidation and respiration. The main and 

 almost sole source of the nitrogen and oxygen present in deep- 

 sea water lies in the atmosphere, and is absorbed there, its 

 quantity being thus dependent on surface conditions of tem- 

 perature and pressure, and not those of the depths. A given 

 quantity of water, having absorbed its oxygen and nitrogen at 

 the surface, may be supposed to sink unmixed with surrounding 

 water to the depths. During the process its amount of contained 

 nitrogen remains constant, whilst its oxygen-supply becomes 

 gradually diminished, owing to the process of oxidation, which 

 in the depths goes on without compensation. That the amount of 

 absorbed oxygen present in sea-water diminishes with the depth 

 has been shown already by Dr. Lant Carpenter's experiments. 

 It is not yet possible to formulate in any precise terms the relation 

 between the depth and the diminution of the oxygen present, 

 but Mr. J. Y. Buchanan's previous conclusion that a minimum 

 of oxygen is a'tained at a depth of about Soo fathoms is not con- 

 firmed by the summing-up of the whole of the evidence now 



' "Official Report on the Scientific Results of the Voyage of H.M.S. 

 Challenger : Physics and Chemistry," v il. i. 



available. This result is not without biological significance, 

 since the existence of this supposed zone with a minimum of 

 oxygen has been used as an argument in favour of the occurrence 

 of especially abundant life at this depth below the ocean- 

 surface. 



Prof. Dittmar finds thai there is nothing characteristic of 

 bottom-waters as such in regard to their absorbed gases, 

 nothing to distinguish them from waters from intermediate 

 depths. This, it seems to me, is not quite what might have 

 been expected, as the concentration of the food-supply, and 

 consequently of life, on the actual bottom might have led to a 

 different result. 



If there were absolute stagnation of the water at great depths, 

 the oxygen might be reduced there to zero, but the fact that in 

 no case has oxygen been entirely absent from any sample of 

 deep-sea water examined proves that a certain motion and change 

 must occur. The smallest amount of oxygen found at all was 

 in a sample of water from a depth of 2,875 fathoms, and 

 amounted to C65 c.c. per litre only, a result long ago published 

 by Mr. Buchanan. Even this, however, may well be sufficient 

 to support life, since Humboldt and Provencal 1 found that 

 certain fish could breathe in water containing only one-third of 

 that quantity of oxygen per litre. In another sample, from 

 1645 fathoms, it was 2'04 c.c. On the other hand, as much as 

 4 '055 c.c. was found in a sample from 4575 fathoms, and 4'39 

 c.c. in one from 3025. Most remarkable, in one instance 

 water from a depth of only 300 fathoms yielded only 1 "65 c.c. of 

 oxygen. Prof. Dittmar admits that there was no lack of anoma- 

 lous results, some, no doubt, due to some extent to imperfection 

 in the apparatus employed in collecting the water. 



In connection with the valuable investigations carried on in 

 the Travailleur and the Talisman by Prof. Milne-Edwards 

 and his associates, French physiologists have lately commenced 

 researches on some of the problems of deep-sea life. 



Experiments have been made by M. Regnard 2 with a view of 

 determining the effects of high pressures, corresponding with 

 those of the deep sea, on various organisms. Yeast, after being 

 exposed to a pressure of 1000 atmospheres, equal to a depth of 

 about 6500 fathoms of sea-water, for an hour, was mixed with 

 a solution of sugar. An hour elapsed before any signs of fer- 

 mentation appeared, and a mixture of yeast and sugar solution 

 did not ferment at all whilst under a pressure of 600 atmospheres, 

 equal to a depth of about 3900 fathoms. Algae, seeds of 

 phanerogamic plants, Infusoria, and even Mollusca and leeches, 

 were found to be thrown into a sort of state of sleep or latency 

 by exposure to similar pressures, recovering from this condition 

 after a shorter or longer period of return to normal conditions. 

 A fish without a swimming bladder, or one with the bladder 

 emptied of air, may be submitted to a pressure of 100 atmo- 

 spheres, equivalent to a depth of 650 fathoms, without injurious 

 effect. At 200 atmospheres, equivalent to a depth of 1300 

 fathoms, it becomes torpid, but soon revives when the pressure 

 is removed. At 300 atmospheres, equivalent to a depth of about 

 2000 fathoms, the fish dies. 



These experiments are of the highest interest. The pressure 

 made use of was obtained by means of water in the absence of 

 air other than that absorbed at the normal atmosphere pressure, 

 and thus the physical conditions produced were _closely similar 

 to those actually existent in the deep sea. They are the first 

 of their kind. 



Prof. Paul Bert's 3 somewhat similar experiments related 

 to a different question altogether — namely, the effect on aquatic 

 organisms of water subjected to the pressure of compressed air. 

 He found that young eels were rapidly killed when subjected to 

 a pressure of only 15 atmospheres, and could not survive one of 

 even 7 atmospheres for any considerable time.' 1 He pointed out 

 the essential difference between the conditions produced in such 

 experiments and those existing in the deep sea, where the charge 

 of oxygen contained by the water has been taken up at the 

 surface at a pressure of one atmosphere only. 



In the experiments on animals made by M. Regnard's method 

 there is the obvious difficulty that the supply of oxygen in the 

 water compressed cannot be renewed during the experiment but 

 must be gradually reduced by respiration, and for this reason it 

 would probably be useless, unless a large quantity of water would 



1 " Snr la Respiration des Poissons," Journ. de Physique, de Ckimie, el 

 cTHistoire Naturelle, t. Ixix. October 1809 p. 268. 



- P. Regnard, " Recherches Experimentales sur I'lnfluence des tres-hautes 

 Pressions sur les Organismes vivants," Comptes Rendus, No. 12. 24 mars 

 1884. p. 745 



3 La Prcssion baromitrique, Paris, 1878, p. 814. 4 Ibid. p. 1151. 



