576 
DR,. SANDERSON ON THE INFLUENCE EXERCISED BY THE 
so long as the two levers are parallel. When therefore great variations of arterial 
pressure take place in the course of an experiment, it is necessary in order to determine 
the synchronism of the events recorded, to adopt some method of marking synchronical 
points in the two tracings inscribed simultaneously on the paper. This object is best 
attained by making simultaneous momentary interruptions by withdrawing the levers 
from the paper at the same instant. With this view the stand on which the lever- 
apparatus and manometer are fixed is so constructed as to have a horizontal rotatory 
movement round a fixed pin, the position of which nearly coincides with the base.of the 
rectangular brass rods on which the bearings of the levers are supported. By this 
movement, which is regulated by a screw, the operator can at will approximate or with- 
draw the points of the brushes. 
2. Experiments as to the relation between the arterial pressure and the 
movements of the thorax in the normal animal. 
The first experiment was made in the Museum of Middlesex Hospital on the 14th of 
September, 1864. The dog having been secured in the usual manner, the dynamometer 
was adjusted to the femoral artery, and as soon as the breathing had become tranquil, a 
mask of gutta percha of a suitable form was placed loosely over his snout and connected 
by a tube with the vulcanite bag. In this preliminary experiment it was observed that 
“ each inspiratory descent of the lever was accompanied and followed by an arterial 
ascent, that is to say, by a succession of short and quick oscillations, which imply that 
during the period they express, the ventricles of the heart became fuller and fuller, their 
systole more vigorous but less complete, and their diastole accelerated ; while in the 
interval between each inspiration and its successor the arterial pressure sank, the con- 
tractions of the ventricles were more rare, and the diastole of longer duration.” 
The investigation was resumed in the physiological laboratory of University College, 
the apparatus having been in the meantime entirely reconstructed. Preliminary expe- 
riments were made on the 2nd, 3rd, 9th, and 11th of March, which yielded results in 
accordance with those previously and subsequently obtained. The apparatus was not, 
however, brought to a satisfactory state of completeness till the end of May, after which 
the observations given in the Plates were made. 
Observation I. — June 10th, 1865 (Plate XXIII. fig. 1). 
A male terrier of moderate size was secured on its back in the usual way, viz. by 
ligatures attached to each extremity. The femoral artery having been exposed, a silver 
canula, previously filled with saturated solution of carbonate of soda, was introduced and 
secured. The trachea was then laid bare about 1 inch from its upper end, and partially 
cut across. A glass tube as large as it would admit was inserted and secured by a liga- 
ture, which was then connected with the caoutchouc hag by means of the T-shaped tube 
above described, while the communication between the artery and the dynamometer was 
