AMPHIBIA. 
or on land. If we confider the words ctu.tpt (utrinque, both 
ways), and ( 3 io; (vita, life), from which the term amphi¬ 
bious is derived ; we fliould undcrftand, that animals hav¬ 
ing; this title are capable of living as well by land, or 
in the air, as by water; or of dwelling in either conflant- 
ly : but it will be difficult to find any animal that can 
fulfil this' definition, by being equally qualified for either. 
Dr. Parlous, therefore, from confidering their oeconomy 
refpeiftively, divides them into two orders, viz. i. Such 
as enjoy their chief functions by land, but occafionally 
go into the water, i. Such as chiefly inhabit the water, 
but occasionally go alhore. What he advances on this 
liibiedt is curious, and well illuftrates the nature of them. 
Of the firft order, he particularly confiders the phocae ; 
and endeavours to (hew, that none of them can live en¬ 
tirely in the water ; but that their chief enjoyment of the 
fundflions of life is on ffiore. Thefe animals, heobferves, 
are really quadrupeds; but, as their chief food is filh, 
they are under a necelTity of going out to lea to hunt 
their prey, and to great distances from ffiore ; taking care 
that, however great the difiance, rocks or fmall iflands 
are at hand, as refting-places when they are tired, or when 
their bodies become too much macerated in the water ; 
and they return to the places of their ufual refort to fleep, 
copulate, and bring forth their young, for the following 
reafoirs, viz. It is well known, that the only ellential dif¬ 
ference (as to the general ftrufture of the he<urt) between 
amphibious and land animals, or fuch as never go into 
the water, is, that in the former the oval hole remains 
always open. Now, in fuch as are without this hole, if 
they were to be immerfed in water for but a little time, 
refpiration would ceafe, and the animal mud die; becaufe 
a great part of the mafs of blood pafles 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 mafs to the head and 
extremities, &c. 
Now-, the blood pafles through the lungs in a continual 
uninterrupted fiream, while refpiration is gentle and mo¬ 
derate ; but, when it is violent, tlpen the circulation is 
interrupted, for infpiration and expiration are now car¬ 
ried to their extent; and, in this fiate, the blood cannot 
pafs through the lungs, either during the total infpira¬ 
tion or total expiration of the air in breathing: for, in 
the former cafe, the inflation comprefl’es the returning 
veins ; and, in the latter, by the collapfion of the lungs, 
thefe veins are interrupted alfo; fo that it is only between 
thefe two violent actions that the blood Can pafs: and 
hence it is, that the lives of animals are fhortened, and 
their health impaired, when they are fubjedf to frequent 
violent refpiration ; and thus it is, that when animals 
have once breathed, they rauft continue to refpire ever 
after, for life is at an end when that ceafes. 
There are three necelfary and principal ufes of refpira¬ 
tion in all land-animals, and in thole kinds that are count¬ 
ed amphibious. The firft is, that of promoting the cir¬ 
culation of ail the blood through the whole body and ex¬ 
tremities. In real fifties, the force of the heart is alone 
capable of fending the blood to every part, as they are not 
furniffied with limbs or extremities ; but, in the others 
mentioned, being all furnifhed with extremities, refpira¬ 
tion is an afllftant force to the arteries in fending blood to 
the extremities; which, being fo remote from the heart, 
have need of fuch afiiftance, othenvife the circulation 
would be very languid in thefe parts : thus we fee, that, 
in perfons fubjeft to afihmatic complaints, the circulation 
grows languid, the legs grow cold and cedematous, and 
other parts fuffer by the defeft of refpiration. A fecohd 
ufe of breathing is, that, in infpiration, the variety of 
particles, of different qualities, which float always in the 
air, might be drawn into the lungs, to be infinuated into 
the mafs of blood, being highly necelTary to contempe- 
rate and cool the agitated mafs, and to contribute refined 
pabulum to the fiper parts of it, which, meeting with the 
daily fu'pply of chyle, ferves to aflimilate and more inti- 
Vo l. I. No. 3 1. 
mately mix the mafs, and render its conftitution the fitter 
for flip porting the life of the animal. Therefore it is, that 
valetudinarians, by changing foul or unwholefome air for 
a five, good, open, air, often recover from lingering dd- 
eafes. A third principal ufe of refpiration is, to promote 
the exhibition of voice in animals ; which all thofe who 
live on the land do, according to their fpecific natures. 
From thefe confiderations it appears, that the phocie of 
every kind are under an abfolute neceflity of making the 
land their principal refidencc. But there is another very 
convincing argument why they refide on ffiore the greatefi 
part of their time; namely, that the flefli of thefe crea¬ 
tures is analogous to that of other land-animals ; and there¬ 
fore, by over long maceration, added to the fatigue of 
chafing their prey, they would fuffer fuch a relaxation as 
would deftroy them. It is well known, that animals which 
have lain long under water, are reduced to a very lax and 
even putrid fiate; and the phoca mull balk in the air on 
fliore : for, while the folids are at refi, they acquire their 
former degree of tenfion, and the vigour of the animal is 
reftored; and, while he has an uninterrupted placid refpi¬ 
ration, his blood is refrelhed by the new fupply of air, 
and he is rendered fit for his next cruife : for action wafies 
tile moll exalted fluids of the body, more or lefs, accord¬ 
ing to its duration and violence ; and the refiorative refi 
mult continue longer or ihorter, according to the quantity 
of the previous fatigue. 
We fliall next examine by what power thefe animals are 
capable of remaining longer under water than land-ani¬ 
mals. All thefe have the oval hole open between the 
right and left auricles of the heart ; and, in many, the 
canalis arteriofus alfo: and, while the phoca remains un¬ 
der water, which he may continue an hour or two, more 
or lefs, his refpiration is flopped; and the blood, n'*. find¬ 
ing the pa Huge through the pulmonary artery free, rufhes 
through the hole from the right to the left auricle, and 
partly through the arterial canal, being a fhort paffage to 
the aorta, and thence to every part of the body, main¬ 
taining the circulation: but, upon rifing to come aihore, 
the blood finds its palfage again through the lungs the 
moment he refpires. Thus the foetus in utero, during 
its confinement, having the lungs comprelfed, and conle- 
quently the pulmonary arteries and veins impervious, lias 
the circulation of the blood carried on through the oval 
hole and the arterial canal. Now, fo far, the phoca in the 
water, and the foetus in utero, are analogous ; but they 
differ in other material circumftances. One is, that the 
foetus, having never refpired, remains fufficiently nouriflied 
by the maternal blood circulating through him, and con¬ 
tinues to grow till the time of his birth, without any want 
of refpiration during nine months confinement: the phoca, 
having refpired the moment of his birth, cannot live very 
long without it, for the reafons given before; and this hole 
and canal would be clofed in them, as it is in land-ani¬ 
mals, if the dam did not, foon after the birth of the cub, 
carry him fo very frequently into the water to teacli him ; 
by which practice thefe paflages are kept open during life, 
othenvife they would not be capable of attaining the food 
defigned for them by Providence. Now, as all fostufes 
have t hefe paflages open, if a whelp of a true water-fpaniel 
were, immediately afterits birth, ferved as the phoca docs 
her cubs, and immerfed in water, to (top refpiration for a 
little time every day, it is probable that the hole and ca¬ 
nal would be kept open, and the dog be made capable of 
remaining as long under water as the phoca. 
Frog's, how capable foever of remaining in the water, 
yet cannot avoid living on land, for they refpire; and, if a 
frog be thrown into a river, he makes to the fliore as fait 
as he can. The lizard kind, fuch as may be called wa¬ 
ter-lizards, are all obliged to come to land, to depofit 
their eggs, to refi, and to fleep. Even the crocodiles, who 
dwell much in rivers, fleep and lay their eggs on fliore, 
and, while in the water, are compelled to rife to the fur- 
face to breathe; yet, from the texture of rheir Italy cpr 
veiing, they are capable of remaining in the water longer 
6 H by 
