THE BLOOD FLOW 



399 



by the plethysmographic method.^ The part to be experimented upon is enclosed 

 in a rigid capsule, known as a plethysmograph, which is then connected with a 

 volume recorder or an ordinary tambour. The shape of this instrument, however, 

 must necessarily be changed to suit 

 the anatomical peculiarities of the 

 organ. We have so far been placed in 

 possession of plethysm ©graphs for the 

 kidney, spleen, heart, lung, liver, brain 

 and the anterior and posterior extremi- 

 ties. Special names have been given 

 to these; the one for the heart being 

 designated as a cardiometer, and the 

 one for the kidney as a kidney 

 oncometer, in contradistinction, for 

 example, to the splenic and hepatic 

 oncometers. 



The principle of plethysmography 

 may be illustrated with the help of the 



cranial cavity. If the skull is trephined, and the trephine-opening connected with 

 a recording drum, the variations in the volume of the brain coincident with the 

 various bodily activities, may be accurately followed upon the paper of a kymo- 

 graph. ^ This same procedure may be practised upon any other organ provided, of 



t 



Fig. 212. — Brodie's Recordek. 

 A, rubber pouch; R, is placed between 

 two plates A and B;the latter is equipped 

 with a writing lever. 



FiQ. 213. — A Schematic Diagram of Mosso's Plethysmograph for the Arms 

 a, The glass cylinder for the arm, with rubber sleeve and two openings for filling 

 with warm water; s, the spiral spring supporting the test tube, t. The spring is so cali- 

 brated that the level of the liquid in the test tube above the arm lemains unchanged as 

 the tube is filled or emptied. The movements of the tube are recorded on a drum by 

 the writing point, p. (Howell.) 



course, that its shape and position permit of its being enveloped by a rigid capsule. 

 Air transmission or fluid transmission may be employed, and the organ may be 



1 For a full description, see : Francois-Frank, in Marey's Traveaux du Labora- 

 toire, 1876. 



2 Suggested by Hallion and Comte, Arch, de Phys. norm, et pathoL, 1894. 



