BY DR. BURDON-S ANDERSON. 259 



vein. The splanchnic nerve may be reached either in the ab- 

 domen or in the thorax. In very exact experiments, and es- 

 pecially in those that relate fco the functions of the afferent 

 fibres, it is obvious)}' desirable that these organs should not 

 IT exposed by opening the peritonaea! cavity; but for the pur- 

 pose of demonstrating the vasomotor functions of the nerve, 

 this precaution is unnecessaiy. When one of the splanchnic 

 nerves is divided in the rabbit, the arterial pressure sinks ; on 

 electrical excitation of the divided nerve, it rises to a height 

 which far exceeds the normal limits. Section of the other 

 nerve is followed by further reduction, which, however, is not 

 so considerable as that produced by division of the first. The 

 reduction of pressure after section is attended with increase, 

 the elevation of pressure after excitation with decrease of the 

 frequency of the pulse. These facts are demonstrated as fol- 

 lows : 



A chloralized rabbit having been secured in the prone 

 position, and one carotid connected with the kymograph, the 

 abdominal cavity is freely opened in the linea alba. The in- 

 tegument is then carefully divided by a transverse incision, 

 which extends outwards from the first incision a little below 

 the edge of the ribs. A curved needle, of the form shown in 

 fig. 203 e, guarded by the left forefinger, is then passed under 

 the abdominal wall in the direction of the incision. Its point 

 having been brought out about two and a half inches from the 

 linea alba, the ligatures are tightened in such a way that the 

 muscles are constricted at different levels. The part between 

 the ligatures is then divided by a horizontal incision, which 

 may be continued in the same direction without hemorrhage. 

 This done, the left splanchnic nerve is plainly seen running 

 down parallel to the aorta on its left side, towards the supra- 

 renal capsule. The space in which it lies is occupied by very 

 loose cellular tissue covered by peritoneum, which must be 

 broken through to get at the nerve. 



Immediately after the abdominal cavity is opened that is, 

 before the nerves are touched there is a very considerable 

 rise of arterial pressure, which is accompanied with slowing 

 of the pulse. These effects are, however, only transitory, the 

 mercurial column sometimes sinking immediately afterwards 

 below its original level. After division of the left splanchnic 

 it sinks very considerably, often as much as forty millimetres 

 (f. e., more than an inch and a half). On placing the peri- 

 pheral cut end between the copper points of the excitor and 

 opening the key, the column suddenly rises. The sinking pro- 

 duced by section of the right nerve is comparatively incon- 

 siderable. As it is very difficult to get at, its division may be 

 omitted, all that is essential in the experiment being observ- 

 able after section of the left. 



