210 RESPIRATION 



duced some of it, along with excess of hydrogen, into a glass 

 "eudiometer" he passed a spark. Instead of the mild explosion 

 usual in air analyses, there was a violent explosion which broke 

 his instrument. He then knew that he had made a most significant 

 discovery, as the gas he was analyzing must be nearly pure oxy- 

 gen. He got another eudiometer and made a number of analyses of 

 gas from the swim bladder. The results showed that while the 

 gas taken from the swim bladder of a fish near the surface often 

 contained less oxygen than ordinary air, that taken from fishes 

 caught at great depths contained nearly pure oxygen. 2 Biot had 

 discovered oxygen secretion. 



To illustrate the real significance of his observations we may 

 take an analysis made much more recently by Schloesing and 

 Richard, 3 in connection with which the depth from which the 

 fish was taken is definitely stated, and was 4,500 feet. They found 

 that the gas contained 84.6 per cent of oxygen, together with 3.6 

 per cent of CO 2 and n.8 per cent of nitrogen. The latter gases 

 are, however, quite likely to have mostly got in by diffusion during 

 the delay before the sample was taken. Now the pressure at 4,500 

 feet is 136 atmospheres. Therefore the oxygen pressure in the 



Q i fZ 



swim bladder was at least I36x = 115 atmospheres, while 



i oo 



the oxygen pressure in the sea water was only about 21 per cent 

 of an atmosphere, and, in the blood circulating in the capillaries 

 round the swim bladder, certainly very much less. At a moderate 

 estimate the oxygen pressure on the inside of the wall of the 

 swim bladder was at least 1,000 times greater than in the cap- 

 illaries outside. 



In the monograph already referred to, Moreau described a 

 number of experiments showing the conditions under which oxy- 

 gen secretion into the swim bladder occurs. He found, for instance, 

 that if a fish confined in an open cage was sunk to a considerable 

 depth, so that its specific gravity became greater than that of the 

 water, it gradually secreted oxygen so as to restore the balance ; 

 and similarly if its swim bladder had been emptied by puncturing. 

 The simple experiment on the goldfish which I have just described 

 is of the same nature. Moreau even found that if a weight was 

 attached to one fish in an experimental tank, and a float to another 

 fish, so that the first fish was for the time glued to the bottom, and 

 the second to the surface, both fishes would soon be swimming 



a Biot, Memoir es de la Societe d'Arcueil, 1807. 

 3 Comptes rendus, Vol. 122, p. 615, 1896. 



