248 CIRCULATION OF THE BLOOD*. 



are below the occipital bone, the effect is uncertain. Lastly, 

 great care must be taken to use feeble currents, and not to pro- 

 long the excitations, for the vasomotor nervous system of the 

 frog is very readily exhausted. 



49. (3.) Excitation and Section of the Spinal Cord in 

 the Rabbit. The requirements and preliminary preparation 

 for this experiment are the following: A canula and subcuta- 

 neous 83 7 ringe for injecting 20 per cent, solution of curare into 

 the jugular vein ; apparatus for a kymographic observation of 

 arterial pressure ; apparatus for artificial respiration ; a needle 

 for ligaturing the muscles, in addition to the ordinary instru- 

 ments. The canula for the jugular is shown in fig. 220 An 

 India-rubber tube is fitted to it, the end of which is closed by a 

 ligature. It is inserted as follows: The rabbit having been 

 placed in the usual way on Czermak's rabbit supporter, with 

 the cushion under its neck, the integument is divided in the 

 middle line from the pomum ^(famtdownwards, as directed in 

 Section I. On drawing the edge of the incision to either side, 

 the jugular vein is readily seen as it crosses the sterno-mastoid. 

 It is then carefully cleared of the platysma fibres and fascia 

 which cover it, and of its sheath to the extent of an inch or 

 more, with the aid of two pairs of blunt forceps. A clip having 

 been placed on the proximal end of the cleared part, a ligature 

 is looped round the distal end, which is tightened as soon as 

 it is seen that the vein is distended. This being accomplished, 

 a second ligature is placed round the vessel between the first 

 ligature and the clip, and then a V-shaped incision is made in 

 the vein immediately beyond it. Finally, the canula, which has 

 been previously filled with saline solution, is slipped into the 

 vein and secured in its place by the ligature prepared for it. 

 When it is intended to inject, the point of the subcutaneous 

 syringe is shrust through the closed tube of India-rubber. On 

 withdrawing it no liquid escapes. The plan has the advantage 

 that successive quantities may be injected with the greatest 

 facility. The mode of preparing the carotid artery, and of con- 

 necting it with the kymographic canula, has been described in 

 34. For the present purpose it is necessary to free the artery 

 from its connections to a greater extent than usual. The canula 

 having been secured in the artery, and the latter divided beyond 

 the point of insertion, the canula is turned back and fixed to 

 the arimal's thorax (by tying it to the fur) in such a position 

 that the artery forms a loop, with its convexity towards the 

 head. The purpose of this arrangement is to prevent the artery 

 from being strained when the animal is turned. The apparatus 

 for artificial respiration has not yet been described. It is re- 

 quired because the animal being under the influence of curare, 

 its voluntary muscles are paralyzed. As a substitute for natu- 

 ral breathing, air must be injected in the proper quantity at 



