394 PRACTICAL PHYSIOLOGY 



become over-distended (Barnard). The pericardium prevents over- 

 distension of the right heart when the abdomen is compressed, or when 

 the body is in the vertical head-down position. 



CHAPTER XLL 

 PLETHYSMOGRAPHS. 



Plethysmographs and Oncographs. The circulation through the 

 various organs is investigated by placing them in an air-tight box. The 

 box is connected with a piston recorder or tambour. The shape 

 of the box, which may be moulded of gutta-percha, is made to fit 

 the organ investigated. In the case of the spleen, for example, a 

 shallow oblong box is made, with a depression at one side to permit 

 the passage of the splenic vessels. The spleen is placed within it 

 and the depression is packed with cotton-wool and vaseline. A 

 vaselined glass lid is then fastened on by rubber bands. A side tube 

 leads from the box to the recording tambour. Similar boxes are 

 made for the left lobe of the liver, a lobe of the lung, a loop of 

 intestine, etc. 



K 



FIG. 254. Diagram of an oncometer and piston recorder. The rubber bauds fasten 

 the glass lid in position. 



Oncometery of the Kidney. A cannula is placed in the external 

 jugular vein of an animal anaesthetised with chloroform and ether. 

 Tracheotomy is performed and the animal curarised. Artificial respira- 

 tion is established and the air is blown through the anaesthetic bottle. 

 The carotid artery is exposed and connected with a mercurial mano- 

 meter. The kidney is exposed by a lumbar incision without opening 

 the peritoneum if possible. The kidney is separated from the peri- 

 nephritic fat and placed in the oncometer. The oncometer is then 

 connected with the oncograph. 



To investigate the flow of urine a fine catheter is tied into the 

 ureter, or else a tube is tied into the bladder and the neck of the 

 bladder closed by a ligature. The flow of urine can be measured 

 in a measure glass or recorded by allowing the drops to fall from 

 the collecting tube on to an aluminium disc attached to a lever. The 



