404 ANIMAL PHYSIOLOGY. 
The Respiration and Circulation in Asphyxia.— A most instruct- 
ive experiment may be arranged thus: 
Let an anesthetized rabbit, cat, or such-like animal, have 
the carotid of one side connected with a glass tube as before 
described (page 229), by which the blood-pressure and its 
changes may be indicated, and, when the normal respiratory 
acts have been carefully observed, proceed to notice the effects 
on the blood-pressure, etc., of pumping air into the chest by a 
bellows, of hindering the ingress of air to a moderate degree, 
and of struggling. With a small animal it will be difficult to 
observe the respiratory effects on the blood-pressure by simply 
watching the oscillations of the fluid in the glass tube, but this 
is readily enough made out if more elaborate arrangements be 
made, so that a graphic tracing may be obtained. 
But the ‘main events of asphyxia may be well (perhaps best) 
studied in this manner : 
Let the trachea be occluded (ligatured). At once the blood- 
pressure will be seen to rise and remain elevated for some time, 
then gradually fall to zero. These changes are contemporane- 
ous with a series of remarkable manifestations of disturbance 
in the respiratory system as it at first appears, but in reality 
due to wide-spread and profound nutritive disturbance. So far 
as the breathing is concerned, it may. be seen to become more 
rapid, deeper, and labored, in which the expiratory phase be- 
comes more than proportionably marked (dyspnea) ; this is fol- 
lowed by the gradual action of other muscles than those usually 
employed in respiration, until the whole body passes into a ter- 
rible convulsion—a muscle-storm in consequence of a nerve- 
storm. When this has lasted a variable time, but usually 
about one minute, there follows a period of exhaustion, during 
which the subject of the experiment is in a motionless condi- 
tion, interrupted by an occasional respiration, in which inspi- 
ration is more pronounced than expiration; and, finally, the 
animal quietly stretches every limb, the sphincters are relaxed, 
there may be a discharge of urine or feces from peristaltic 
movements of the bladder or intestines, and death ends a strik- 
ing scene. These events may be classified in three stages, 
though the first and second especially merge into one another: 
1. Stage of dyspnoea. 2. Stage of convulsions. 3. Stage of 
exhaustion. 
It is during the first two stages that the blood-pressure rises, 
and during the third that it sinks, due in the first instance 
chiefly to excessive activity of the vaso-motor center, and. in 
