138 PHILOSOPHICAL TRANSACTIONS. [aNNO ISqG-*. 



On the Structure of the Internnl Paris of Fish. By Dr. Charles Preston. 



N°225, p. 419. 



The principal difference between fish and other animals, is their want of 

 lungs and respiration ; whereas all other animals have lungs, both terrestrial, 

 volant, and amphibious ; and in insects, the several tracheae, that are spread 

 throughout the whole body, serve them instead of lungs. And yet it is 

 necessary that something should supply this in fishes, which may have the 

 same effect on their blood, as the air has upon ours, by entering into our 

 lungs ; viz. to divide and dissolve it, and render it fit for circulation. Now 

 we find no part in fish more proper to produce this effect than the bronchia, 

 that lie like so many leaves over each other under their gills ; for they 

 receive the water in by the mouth, and return it by the gills ; or receiving 

 it in by the gills, they throw it out by the mouth. 



Now it is agreed upon by all, that the water contains something that pro- 

 duces this effect : and this seems most probably to be the air contained in the 

 water, that dissolves the blood in the bronchia of fish, as well as it does that 

 in the lungs of all other animals. That there is air in all water, cannot be 

 doubted, after the experiment of M. Marolle. He set a vessel of water over 

 the fire, so as to drive out the air from it ; This water he put into the air 

 pump, to extract the air from it ; and after that filled a phial with it, within 

 two or three fingers of the top, which space he left only full of air, and 

 stopped the phial well : and by shaking it, the water imbibed the air, so as to 

 rise up and quite fill the phial. 



It may be objected, that if tVie air in the water were the cause of this effect, 

 the fish would live in the open air. I shall only reply to this, that fish have 

 tbeir blood naturally less hot than ours, so that the natural heat of our blood 

 would in them be a fever and mortal ; hence we need not wonder they can- 

 not live in the air ; for the nitre* of the pure air is in too great a quantity, and 

 too subtle, so as it dissolves their blood too much, and makes it too fluid: 

 whereas the nitre* in the water is more gross, and in less proportion : whence it 

 gives their blood only a fluidity requisite to keep it in its natural state. To 

 prove that it is in the bronchia that this division is performed, we need only 

 observe their extraordinary redness above any other part of the body, a proof 

 that the blood is there more divided :-|~ fish are also fuund to die in water frozea 

 over, which happens plainly from their communication with the external air 

 being hindered by the ice. 



• Oxygen. t Or, as physiologists now sny, more oxygenized. 



