748 eepobt — 1884. 



In connection with the valuable investigations carried on in the ' Travailleur ' 

 and the ' Talisman ' by Professor Milne Edwards and his associates, French physio- 

 logists have lately commenced researches on some of the problems of deep-sea 

 lite. 



Experiments have been made by M. Eegnard 1 with a view of determining the 

 effects of bigh pressures, corresponding with those of the deep sea, on various 

 organisms. Yeast, after being exposed to a pressure of 1,000 atmospheres, equal to a 

 depth of about 6,500 fathoms of sea-water, for an hour, was mixed with a solution of 

 sugar. An hour elapsed before any signs of fermentation 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 3,900 fathoms. Algae, seeds of a phanero- 

 gamic plant, 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 atmospheres, equivalent to a depth of 650 fathoms, 

 without injurious effect. At 200 atmospheres, equivalent to a depth of 1,300 

 fathoms, it becomes torpid, but soon revives when the pressure is removed. At 300 

 atmospheres, equivalent to a depth of about 2,000 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. 



Professor Paul Bert's 2 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. 3 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 under a pressure of one atmosphere ouly. 



In the experiments on animals made by M. Begnard's method there is the 

 obvious difficulty that the supply of oxygen in the water compressed cannot be re- 

 newed 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 

 be employed, to try the effect on a fish of a very gradual application of pressure, 

 extending over many hours. It is probable that the results would be greatly 

 modified if plenty of time could be given for the fish to accommodate itself to the 

 change of pressure, and the conditions in which it moves in nature slowly from one 

 depth to another be imitated. The results of M. Eegnard's further experiments 

 will be looked forward to with great interest. 



A question of the utmost moment, and one that has received a good deal of 

 attention, is that as to the source of food of the deep-sea animals. Certainly a 

 large proportion of this food is derived from the life on the ocean-surface. The 

 debris of pelagic animals sinks slowly downwards, forming on its passage a sparsely 

 scattered supply of food for any animals possibly living at intermediate depths, 

 but becoming concentrated as it were on the bottom. The pelagic animals depend 

 for their ultimate source of food, no doubt, largely on the various pelagic plants, 

 the range of which in depth is limited by the penetration of sea-water by the sun- 

 light, and probably to an important extent is dependent on the symbiotic com- 

 binations of radiolarians with zooxanthella. But a large part of their food-sup- 

 ply is also constituted by animal and vegetable debris derived from the coasts, 

 either directly from the littoral zone or by rivers and the action of the tides from 

 terrestrial life. Immense quantities of shore-de"bris have been dredged from deep 

 water near coasts, and deep-sea life appears to diminish in abundance as coasts are 



1 P. Kegnard, ' Rechercbes Experimentales sur l'lnfluence des tres-hautes Pressions 

 sur les Organismes Vivants,' Comjites-Sentfiis, No. 12, 24 mars 1884, p. 745. 

 • La Prcssi.on BaromHrique, Paris, 1878, p. 814. 

 3 Ibid. p. ] 151. 



