BY DR. BURDON-SANDERSON. 251 



sinks from, say, 100 millimetres to 20 or 30. One needle is 

 then inserted in the middle line above the posterior tubercle 

 of the atlas, the other below it, the key being closed. On 

 opening the latter so as to direct the induced current through 

 the needles, the arterial pressure rises to a height which at 

 first equals, if not exceeds, that at which it stood before sec- 

 tion. 



The effects of exciting the cord in increasing the arterial 

 pressure are seen with equal distinctness when the cord is not 

 previously divided. In both cases the ascent is accompanied 

 with an increase of the frequency of the contractions of the 

 heart, the cause of which will be investigated in a future sec- 

 tion. 



Direct Observation of the Arteries during Excitation of the 

 Cord. That the increase and diminution of arterial pressure 

 observed is in great part, if not entirety, dependent on con- 

 traction of the arterial systems, can be shown in several ways. 

 The most direct consists in the observation of the arteries 

 themselves. In the rabbit, the arteria saphena, which, after 

 leaving the femoral, just as that vessel enters the adductor 

 sheath, takes a superficial course towards the inner side of the 

 knee, may be observed with great facility. All that is neces- 

 sary is to divide carefulty, first the skin, and then the fascia 

 which covers it : the two saphena veins which lie on either 

 side of it serve to determine its exact position. In this 

 artery it can be readily seen that as the pressure rises the 

 vessel contracts. To observe the effect of vascular contrac- 

 tion on the heart, that organ must be exposed. In a curarized 

 animal, this can be effected without interfering materially with 

 the vital functions. Ligatures of fine copper wire having 

 been passed, with the aid of a curved needle (fig. 203, e), 

 around the 3d, 4th, 5th, and 6th cartilages, close to the left 

 edge of the sternum, and a second vertical series of ligatures 

 around the corresponding ribs at a sufficient distance outwards, 

 the portion of the thoracic wall which lies between the two 

 series can be removed without hemorrhage. It is then seen 

 that after section of the cord, the heart is flaccid and empty, 

 and that its cavities fill and its action becomes vigorous when 

 the vascular contraction caused by excitation of the peripheral 

 end forces the blood forwards so as to fill the right auricle. 



[For the experimental proof that the effects of excitation 

 of the cord above described are not dependent on the increased 

 vigor of the contractions of the heart, see 80, 81.] 



50. (4.) Section of the Medulla Oblongata in the 

 Rabbit, within the Cranium. The recent experiments of 

 Liuhvig and Owsjannikow have shown that the medulla may 

 be divided within the cranium with the same results as regards 

 arterial pressure as are obtained when it is severed immediately 



