

OH. xxi.] THE ONCOMETEH. 3CX) 



2. The method of slowly interrupted shocks. If a mixed nerve 

 is stimulated with the usual rapidly interrupted faradic current, 

 the effect is constriction ; but if the induction shocks are sent 

 in at long intervals (e.g. at intervals of a second), vaso-dilatator 

 effects are obtained. This can be readily demonstrated on the 

 kidney vessels by stimulation of the anterior root of the eleventh 

 thoracic nerve in the two ways just indicated. 



3. The influence of temperature. Exposure to a low tempera- 

 ture depresses the constrictors, more than the dilatators. If the 

 leg is placed in ice-cold water, stimulation of the sciatic, even 

 if it has only been recently divided, produces a flushing of the 

 skin with blood. ' { 



The action of vaso-motor nerves can be studied in another 

 way than by the use of the mercurial or other forms of mano- 

 meter, which is the only method we have considered so far. 

 The second method, which is often used together with the 

 manometer, consists in the use of an instrument which records 

 variations in the volume of any limb, or organ of an animal. 

 Such an instrument is called a plethysmograph. One of 

 these instruments applied to the human arm is shown in the 

 accompanying figure (fig. 289). 



Every time the arm expands with every heart's systole, a little 

 of the fluid in the plethysmograph is expelled and raises the 

 lever. Variations in volume due to respiration are also seen in 

 the tracing. An air plethysmograph connected to a Marey's 

 tambour gives' equally good results. 



The same instrument in a modified form applied to such organs 

 as the spleen and kidney is generally called an oncometer, and 

 the recording part of the apparatus, the oncograph. These 

 instruments \ve owe to Prof. Roy, and the next two figures represent 

 respectively sections of the kidney oncometer and oncograph. 



Each consists of a metal capsule, of shape suitable to enclose 

 the organ : its two halves are jointed together, and fit accurately 

 except at one opening which is left for the vessels of the organ. 

 A delicate membrane is attached to the rim of each half, the 

 space between which and the metal is filled with warm oil. The 

 tube from the oncometer is connected to the oil-containing cavity 

 of the oncograph by a tube also containing oil. An increase in 

 the volume of the organ squeezes the oil out of the oncometer 

 into the oncograph and so produces a rise of the oncograph piston 

 and lever; a contraction of the organ produces a fall of the lever. 



Very good results are obtained by using saline solution instead 

 of oil ; and Prof. Schafer has recently shown in connection with 

 the spleen that a spleen box of simple shape covered with a glass 



