188 ON THE NATURE AND PRINCIPLES OF 



a change in the condition of the heart, or of the 

 .-mailer vessels, both which changes arc continually 

 occurring, it may, in the same individual, be at one 

 time so slight as to be incapable of accomplishing its 

 healthy uses, while at another period its distending 

 power may l;e BO < msiderable, as to rupture some of 

 the containing vessels, and thus threaten the de- 

 struction of life." 



The present communication having for its chief 

 object the elucidation of the pathology of those forms 

 of disordered circulation which consist essentially in 

 a general or partial obstruction to the proper passage 

 of the blood, we cannot here consider those cases in 

 which, from a deficient accumulation of fluid in the 

 aorta, the functions dependent on the distension of 

 its clastic walls are imperfectly performed. But the 

 omission of any further allusion to this point is the 

 more excusable, as this disorder is perhaps more 

 interesting, from its presenting an instance of the 

 confirmation of a physiological law by pathological 

 phenomena, than important as an agent operating in 

 the production of structural disease. 



From the principles previously established it 

 follows, very evidently, that an increased lateral 

 pressure of the blood contained in the aorta can 

 only arise from one or other of two classes of causes 

 viz., either from causes which tend to induce a 

 more rapid influx of blood by quickening the con- 

 tractions of the ventricle, or from circumstances 

 calculated to diminish the efflux of arterial blood by 

 affecting the calibre, through the contractility, of 

 the minute discharging tubes. And causes of each 



