GRAVITY, PRESSURE, AND SOUND 



137 



compressible body, one that contains air en- 

 cased in a more or less readily collapsible 

 shell, will fall more rapidly with increasing 

 depth. Cork and wood, because of the air 

 contained in their cells, are good floats at 

 the surface, but not at great depths, because 

 the walls have collapsed under heavy pres- 

 sure (Murray and Hjort, 1912; Johnstone, 

 J923). 



The rate of falling of animal bodies and 

 of animal excreta is important, because they 

 are the external source of food for bathy- 

 pelagic and benthic animals. A sinking 

 velocity of 100 meters an hour will bring 

 a body to the bottom in most places in less 

 than two days (Krogh, 1934). 



Pressure alters solubility, ionic dissocia- 

 tion, and surface tension in complex fash- 

 ions even for inorganic solutions. As a gen- 

 eral rule, pressure increases dissociation in 

 weak solutions and, in theory, increases the 

 surface tension. Change in solubility de- 

 pends on the solvent and solute that are 

 exposed to pressure (Cattell, 1936). 



The eflFect of increased pressure upon 

 the velocity of chemical reactions of hquids 

 has been investigated for a number of or- 

 ganic chemicals, and some data are avail- 

 able for the pressures within the ecological 

 range; more often the experimental pres- 

 sures greatly exceed 1000 atmospheres. In 

 general, the following rules appear to hold: 



1. Reactions that proceed slowly in the 

 absence of catalysts at a pressure of one at- 

 mosphere show an increased velocity at the 

 same temperature under higher pressure. 

 Rates of reaction may be increased from 

 five to ten times by an increase of 3000 

 atmospheres. 



2. Reactions that do not proceed at a 

 pressure of one atmosphere in the absence 

 of catalysts, similarlv do not proceed at 

 pressures up to 3000 atmospheres. 



There is less evidence concerning the 

 effect of increased pressures in aqueous so- 

 lutions. Such reactions may be accelerated 

 or retarded bv pressure, depending on the 

 catalyst concerned. Acid inversion of cane 

 sugar is decreased in velocity by about 5 

 per cent when subjected to a pressure of 

 500 atmospheres (Fawcett and Gibson, 

 1934). 



The influence of pressure on viscosity 

 varies with the liquid tested: viscosity usu- 

 ally increases with pressure. Water is an ex- 

 ception since, at low temperatures and 

 within the ecological pressure range, it 



shows a decreased viscosity under pressure. 

 When salinity and temperature are disre- 

 garded, the probable difference between 

 viscosity at the surface and at a depth of 

 10,000 meters is so slight as to be negli 

 gible; hence pressure exerts no significant 

 influence on viscosity in the oceans (Sverd- 

 rup, Johnson, and Fleming, 1942). 



EFFECTS OF PRESSURE ON ORGANISMS* 



It is even harder to summarize the results 

 that pressures, such as occur in the ocean, 

 produce on animal life than it is to outline 

 the physical changes such pressures make 

 on the ocean. It is interesting and probably 

 a significant comment on the current lack 

 of information on the possible ecological 

 effect of pressure in the ocean, that Sverd- 

 rup, Johnson, and Fleming (1942) do not 

 discuss pressure in their chapter on "Ani- 

 mals in Relation to Physical-Chemical Prop- 

 erties of the Environment." Knowledge is 

 particularly lacking of the ecological effects 

 produced by high pressures acting over long 

 periods of time. There are indications that 

 many physiological processes continue un- 

 changed in pressures no greater than those 

 found in the ocean. Gastric and pancreatic 

 juices, for example, retain their activity 

 throughout this range. The action of some 

 bacteriophages is retarded by exposure to 

 1000 atmospheres pressure for forty-five 

 minutes, that for staphylococcus being thus 

 affected. Others are unchanged by this pres- 

 sure range even when they are sensitive to 

 super-normal pressures such as are readily 

 applied in the laboratory. Some yeasts fail 

 to carry on fermentation at 600 atmos- 

 pheres, although they recover complete ac- 

 tivity after decompression, even after ex- 

 posure to 1000 atmospheres. Similarly, 

 the prolonged application of 700 atmos- 

 pheres retards putrefaction of a variety of 

 organic substances well contaminated with 

 putrefactive bacteria; many bacteria are un- 

 affected by brief exposure to much greater 

 pressure. 



Increased pressure has no effect on the 

 activity of many protozoans until approxi- 

 mately 250 atmospheres are reached. This 

 pressure causes a cessation of movement in 



* The ecological literature in this field is not 

 extensive. Regnard's summary (1891) is still 

 useful. Hill's monograph (1912) covers a part 

 of the field, and Cattell (1936) 2;ave a schol- 

 arly view of some ecological and certain more 

 narrowly physiological aspects. 



