64. PROF. LIONEL S. BEALE, F.R.C.P., F.R.S., ON VITALITY. 
same time formed and is ready to circulate in the vessels 
also developed very early. Again, the heart, if it is in good 
order, is the most remarkable organ for undertaking a 
varying amount of work without damage. It may be called 
upon at any time to perform much more than double its 
ordinary work in a given time, If you run for a short 
distance you will find the heart beats twice, or more than 
twice, as quickly as ordinarily, the number of beats rising to 
one hundred and twenty or more per minute; and if the 
heart is healthy, and we rest for four or five minutes, it will 
generally be found to have returned to its normal rate of 
action. If at any time you find the increased action goes 
on for long it is very desirable uot to allow the heart to be 
again unduly excited. There are people whose hearts are so 
sound and strong that they can do at the age of sixty or 
seventy almost as much as at twenty; but such organisms 
are not very common. 
The heart requires no attention, no direction, and no 
thought on our part. Many of us unless we feel our pulse 
or put our hand where the heart is situated are not 
conscious that we have a heart steadily working without 
interruption, day and night, from months before birth to 
death, at the average rate of sixty or seventy beats per 
minute. The heart does an enormous amount of work, and 
when we consider the circulation in the case of large 
animals—for instance, the elephant or the whale—the 
amount of work done by the heart is indeed enormous, each 
forcible contraction driving the blood through the vessels 
continually—contractions succeeding one another at certain 
short but definite intervals during the whole hfe of the 
creature. 
I can only brietly refer incidentally to a few points m 
connexion with the structure of the heart; but the mquiry 
is of the greatest interest as regards the principles and 
nature of nervous and muscular action. A very thin section 
must be made; or, better, you may appeal to some small 
animal, parts of whose heart are naturally so thin and 
transparent that a section is not required. In my favourite 
little Hyla viridis, or Green Tree Frog, which is better 
known in Germany than in England, I have seen perfectly 
what I have seldom demonstrated in other animals. 
The Hyla is a beautiful little creature with tactile tips to 
each toe, acting like suckers, so that it can stick to the 
smoothest surface of leaves or even of glass. It jumps, for 
