EXCHANGE OF COLD-BLOODED ANIMALS. 



70S 



recent experiments by Mengarini 1 show that the goldfish (Carassius auratus) 

 and roach (Leuciscus), in which there is a dtictus pneumaticus, the mullet 

 (Mugil cephalus) and rockling (Motella), in which there is no duct, do take up 

 hydrogen from water saturated with that gas. 



Moreau 2 has shown that the withdrawal of the gas of the swimming-bladder 

 by means of a trocar leads in a short time to the secretion of a gas richer in 

 oxygen, and that by a repetition of this process the percentage of oxygen can be 

 raised as high as 85 ; he also states that section of the sympathetic nerve hastens 

 the process of secretion. These observations have been repeated and extended 

 by Hiifner 3 and Bohr. 4 Cod-fish (Gadus callarias) were caught in a net at a 

 depth of about 14 metres (46 feet), and when they were drawn to the surface 

 the gas in the air-bladder expanded so much that the fish swam with their backs 

 downwards. The gas was found in one case to contain 52 per cent, of oxygen ; 

 but when the fish had been near the surface of the water for some time only 13 

 per cent, of oxygen was obtained. After the removal of the gas from the bladder, 

 its secretion begins again : within six hours a little gas has accumulated, and in 

 twenty-four hours the bladder is again full. The rapidity of the process and the 

 increase in the percentage of oxygen is shown by the following examples : 



Bohr has also shown that after section of the branches (rami intestinales) 

 of the vagus which- supply the air-bladder, the secretion of the gas ceases en- 

 tirely, but that no effect upon the secretion is observed after section of the 

 rami cardiaci or the nervi laterales. These phenomena observed in, the case of 

 the swimming-bladder can at present be explained only as a process of secretion. 

 The air is not swallowed, for the fishes with the greatest percentage of oxygen 

 in their bladders are those which do not come to the surface, but live at great 

 depths ; in some of them, moreover, such as the cod (Gadus callarias), there is 

 no communication between the bladder and the mouth. The phenomena can- 

 not be accounted for by simple diffusion, for the water which surrounds 'the fish 

 cannot have a higher tension of oxygen than 21 per cent, of an atmosphere. 5 

 Further, Bohr has shown that the percentage of oxygen is not reduced by 

 diffusion outwards, for when the secretion of fresh oxygen is prevented by 

 section of the vagus, the high percentage of oxygen is maintained 'for "two or 

 three days. As long as the swimming-bladder is fresh, it is almost im- 

 permeable to oxygen, even when the difference of pressures inside and outside 

 the bladder amounts to one atmosphere. It is to be noted .that .the. membrane 

 lining the swimming-bladder has a peculiar glandular structure. 



l Arch.f. Phytiol., Leipzig, 1889, S. 54. 



2 Cotnpt. rend. Acad. d. sc., Paris, 1873, tome Ivii. pp. 37, 816 ; "Recherches experi- 

 mentales stir les i'unctioiies de la vessie natatoire," Paris, 1876 ; " M6m. de physiol.," Paris 

 1877, pp. 69-86. 



3 Arch.f. Physiol. , Leipzig, 1892, S. 54. 



4 Journ. Physiol., Cambridge and London, 1894, vol. xv. p. 494 ; Compt. rend. Acad. 

 d. sc., Paris, 1892, tome cxiv. p. 1560. 



5 Biot, Delaroche, Moreau, loc. cit. ; Jakobsen, Ann. d. Chem. u. Pkarm., Bd. clxvii 

 S. 1 ; Hiifner, Arch.f. PhysipL, Leipzig, 1897, S. 112. 



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