158 SEVENTH REPORT—1837. 
it was easy by a pretty equal pressure to cause a murmur at 
both points. 
With a stout Caoutchouc tube, two feet long and one inch in 
internal diameter, the same results were obtained, but in a more 
remarkable degree, in consequence of the increased size of the 
tube. When the current was strong and the pressure on the 
tube considerable, sounds were produced loud enough to be heard 
without applying the stethoscope or the ear ; and the vibrations 
of the tube below the obstruction were so strong that they threw 
the water in little jets from the outside of the tube. 
In making this experiment, the pressure of the water sudden- 
ly distended a portion of the tube into a globe about three inches 
in diameter, constituting a good imitation of a circumscribed 
true aneurism. As long as the force of the current was suffi- 
cient to keep the walls of the dilated portion tense, no sound 
was heard in them ; but when these walls became flaccid, the 
passing current caused a kind of fremitus in them. Pressure 
on the dilatation, or bending the tube so as to form an angle at 
this point, also sometimes occasioned a murmur. 
A globular India-rubber bottle, three inches in diameter, being — 
adapted to an aperture in the side of a tube half an inch in dia- 
meter, so as to form an elastic sac communicating with it, a 
current was directed through it and all the air expelled. The 
same was done witha tube three-eighths of an inch in diameter, 
and a bottle of an inch and a half. In some positions of the 
tube, the current in passing the lateral ‘sac caused a fremitus ; 
but in others, as when the tube was straight, there was no sound. 
A sudden increase of current, or the removal of external pressure 
from the sac, occasioned a whizzing by the entry of water into 
the sac. Independently of the current, sudden forcible pressure 
caused a whizzing with the expulsion of the fluid, anda similar — 
whizzing attended the rapid reflux into the sac, on the removal 
of the pressure. 
Some of these experiments were repeated with water, rendered 
somewhat viscid with size. The results differed only in requi- 
ring a stronger force of current to produce the same effect. 
Remarks and conclusions. 
From all these results, it is sufficiently plain that a certain re- 
sistance or impediment to a liquid current is the essential phy- 
sical cause of all murmurs produced by the motion of fluids in | 
tubes. That any condition of the walls of the tube beyond the 
impeding point is not, as it has been supposed, essential to the. 
production of these sounds, is proved by the fact that they may 
be produced by a partial obstruction at the terminal orifice of 
