VOL. LVI.] PHILOSOPHICAL TRANSACTIONS. 325 



that the only essential difference, (as to the general structure of the heart), be- 

 tween amphibious and mere land animals, or such as never go into the water, is 

 that in the former the oval hole remains always open. Now, in such as are with- 

 out this hole, if they were to be immersed in water for but a little time, respi- 

 ration would cease, and the animal must die ; because a great part of the mass of 

 blood passes from the heart, by the pulmonary artery, through the lungs, and by 

 the pulmonary veins returns to the heart ; while the aorta is carrying the greater 

 part of the mass to the head and extremities, &c. Now the blood passes through 

 the lungs in a continual uninterrupted stream, while respiration is gentle and 

 moderate ; but when it is violent, then the circulation is interrupted, for inspira- 

 tion and expiration are now carried to their extent ; and in this state the blood 

 cannot pass through the lungs either during the total inspiration or total expi- 

 ration of the air in breathing ; for in the former case the inflation compresses the 

 returning veins, and in the latter, by the collapsion of the lungs, these veins are 

 interrupted also ; so that it is only between these two violent actions that the 

 blood can pass : and hence it is that the lives of animals are shortened, and their 

 health impaired, when they are subjected to frequent violent respiration ; and 

 thus it is that in animals who have once breathed, they must continue to respire 

 ever after ; for life is at an end when that ceases. 



There are 3 necessary and principal uses of respiration in all land animals, and 

 in these kinds that are counted amphibious ; the first is that of promoting the 

 circulation of the blood through the whole body and extremities ; in real fishes, 

 the force of the heart is alone capable of sending the blood to every part, as they 

 are not furnished with limbs or extremities ; but in the others mentioned, being 

 all furnished with extremities, respiration is an assistant force to the arteries in 

 sending blood to the extremities, which, being so remote from the heart, have 

 need of such assistance ; otherwise the circulation would be very languid in these 

 parts ; thus we see, that in persons subject to asthmatic complaints, the circula- 

 tion grows languid, the legs grow cold and oedematous, and other parts suffer by 

 the defect in respiration. A second use of breathing is that, in inspiration, the 

 variety of particles of different qualities, which float always in the air, might be 

 drawn into the lungs, to be insinuated into the mass of blood, being highly 

 necessary to contemperate and cool the agitated mass, and to contribute refined 

 pabulum to the finer parts of it, which, meeting with the daily supply of chyle, 

 serves to assimilate and more intimately mix the mass, and render its constitution 

 the fitter for supjxjrting the life of the animal. Therefore it is, that valetudina- 

 rians, by changing foul or unwholesome air for a free, good, open air, often re- 

 cover from lingering diseases. And a third principal use of respiration is, to 

 promote the exhibition of a voice in animals ; which all those that live on the 

 land do according to their specific natures. 



