MEMOIR OP BARON HALLER. 37 
bilityistoosoft. Some polypi, though very soft, are 
so irritable as to be affected even by the light. 
Irritability then, is a property of animal fibre, in 
the same way as attraction and gravity are properties 
of matter in general ; and all that can be done is 
to explain the phenomena presented by this quality 
of fibre, without entering into useless speculative 
inquiries. 
We may add, that to Haller we apparently owe 
the discovery that the iris is not muscular. His 
words are, “ You will be surprised to learn that the 
iris has no irritability, when the cause of irritation 
applied is mechanical. I have observed that its 
dilatation does not depend upon muscular force. 
After death it still remains dilated ; and the phe- 
nomena presented in animals, whether cold-blooded 
or hot, harmonize with this view.” 
Such, then, is a very short analysis of one of 
Haller’s treatises on this important subject; and 
instead of here expressing any opinion of our own 
concerning it, we shall subjoin a few sentences 
which embody the opinion of the celebrated Tissot, 
who took an early opportunity of introducing it to 
the notice of his countrymen in a French translation. 
“ The great discovery of the present day is irritability, 
described in the accompanying treatise ; in praise of 
which I shall say nothing, seeing its celebrated 
author, for these twenty years past, has favoured 
the public with so many excellent performances, 
and now this subject is become the principal topic 
of all those who devote themselves to the important 
