PROF. LIONEL S. BEALE, F.R.C.P., F.R.S., ON VITALITY. 65 
its size,a long distance. It is of a beautiful green colour, 
changing from light green to dark greenish brown, and may 
easily escape notice on a leaf. Many of these animals are 
brought over to England every year,and people keep them 
as pets and feed them with flies. 
The muscular walls of the auricle of the heart of the 
Hyla are so wonderfully thin that you cau easily see the 
delicate individual muscular fibres and the finest nerve fibres 
distributed near to, and over and under them. Such thin 
tissue in its natural state is far better than any section that 
can be made, and if the extremely thin tissue is properly 
prepared and preserved in glycerine you can see all the 
different structures, and can make out distinctly the relation 
of the delicate nerves and their bioplasts to the muscular 
tissue, and can form some idea of the manner in which they 
act on the muscular fibres. You may in such a specimen 
work out a number of disputed points in connexion with the 
ultimate nerve network and its relation to muscular fibres 
and judge how it acts. These anatomical facts are of great 
interest and importance. 
One cause of the difficulty in forming a conception of the 
changes which take place in living things generally arises 
from the misapprehension that every part of a living 
organism is alive at any one moment. This is a great mistake, 
for the greater part even of a single hair or feather for 
instance is as dead while yet connected with the living 
organism as it is after the severing action of a pair of 
scissors. The free end of a nail which is almost dry, is just 
as dead before it is removed by the knife as it is after the 
free portion is cut away from the rest of the nail. This is, 
of course, a rather important matter, if we bear in mind 
that a similar statement holds good with regard to the 
internal tissues of the body. Parts of the fibrous tissues, 
and many other tissues, such as the dentine and enamel of 
fully formed teeth, are just as far removed from the living 
state while they remain part of the living body as at any 
time after they have been removed. 
Another source of confusion as regards “life” and “ living ” 
is the idea that the tissues of the whole living body are 
absorbed and removed in a certain moderate and definite 
period of time. We used to be assured that every part of 
us Was removed and renewed once in each period of about 
seven years. Now that this is a fallacy is easily proved. 
The actual enamel of the tooth formed during childhood 
F 
