THE FROG PRESSURE FALLACY. 
741 
Though bold and prominent to the eye, its structure is thin and 
deceitful; and, as to the sensitive (or fatty) frog, its formation is 
truly of constricted layers of elastic ligament, well calculated to 
receive pressure from above, but not to communicate it from below. 
In short, the foot expands from superincumbent pressure, while the 
real office of the frog is to permit, yet restrain, this action. 
Now let me inquire, Can you, by using force upon a soft body, 
dilate and expand a harder one! Would you use a wedge of 
dough (or fatty matter ) to cleave a block of wood? But, observed 
the ingenious and subtle lecturer, “ it should be known” that soft 
bodies, when confined, resist with the same force as hard ones. 
“ If,” said he, “ if the objectors were aware of this law of na- 
ture, they would then comprehend how the frog, when pressed 
between the ground, the shoe, and the superincumbent weight, 
performs the functions which I ascribe to it.” Now, Sir, we are 
aware, of course, that fluids, when hermetically sealed, may resist 
in such a manner; but the material flaw in his argument is this, 
that the frog is by no means in a similar situation; on the contrary, 
Nature has so liberally provided it with deep clefts and commis- 
sures, and a structure so guarded against compression, that it can 
relieve itself on all sides: and such are its powers in this respect, 
that even the Professor’s squeezing shoes may for a short time be 
borne. 
Such learned sophisms may do well enough to astonish tyros; 
and it is in this manner he has proceeded, by the help of misplaced 
analogy and perverted reasoning, through repeated discourses, 
bewildering a subject which might be clearly explained in a single 
lecture. Frequently, also, his hearers have been favoured with an 
unhappy substitution of cause for effect, and vice versa. Thus 
“ animals with light heads and necks, thin shoulders, and low ac- 
tion” (viz. our high-bred horses) “ have their frogs high placed and 
small ; ergo, their contraction and their sufferings depend upon the 
want of pressure on the frog.” 
On the contrary, “ those with heavy fore quarters and high ac- 
tion (i. e. our coarse-bred trotters) “ have their frogs low and large; 
ergo, their action and circular feet are consequent on receiving 
more pressure on the frog.” 
Now what is all this but a difference in breeds, in the kind of 
labour and treatment they undergo, and, above all, in their dif- 
ferent susceptibility to the fettering and ruinous effects of the 
common-nailed shoe ? 
But the true expansive action of the foot had ever been, as it 
were, a sealed book to the Professor. “ Cause pressure,” he cried 
(overlooking this principle and the operation of four Jfixed nails 
on each side,) “ and the frog will be forced upward, distend the 
