128 
ON THE SPHYGrMO GRAPH, OR PULSE- RECORDER. 
By A. H. GARROD, B.A., Eellow of St. John’s Coll., Camb. 
I T seems to be an impression with the public generally that 
the science of physiology is so intimately connected with 
medicine, that without a considerable amount of information 
on the latter subject, little or no progress can be made in the 
former. The same idea used to prevail with reference to 
chemistry, until, not many years ago, it gradually became 
apparent that it had an independent existence of its own, and 
might be studied by itself with much advantage. This current 
impression about physiology is no doubt a false one ; and there 
is no more reason against any individual, with spare time at 
his disposal, devoting some of it to physiology, than that he 
should direct his attention to botany, ornithology, geology, or 
any of the subjects which are associated with them. 
In the present paper it is my endeavour to explain the con- 
struction of an instrument, which has been known for a little 
over ten years, and which, from the comparatively little use 
that has been made of the facts which it discloses, has the 
advantage of leaving a large field for future work, open espe- 
cially to those who are of a mathematical and mechanical turn 
of mind. 
Until the time of the illustrious Harvey, the true action of 
the heart, and the use of the several large blood-vessels which 
are connected with it, were very incompletely understood. It 
was known that the heart pulsated, and sent blood out of its 
cavities into some of these vessels, and also that all the vessels 
were not alike ; in fact, that there were two kinds of blood- 
vessels, those with thicker coats of a light yellow colour being 
called arteries, because they were supposed to contain air, and 
those with thinner and less yellow coats, called veins. It was 
also known that on cutting across some of these vessels, as in a 
deep wound, blood spirted in fountain-like jets ; whilst in 
opening the veins of the surface of the arm the blood flowed in 
a slower and much more uniform stream. It was Harvey who 
showed, from the manner in which the valves of the heart were 
