lyii EXPERIMENTAL PHYSIOLOGY 



not constricted. The junction with the lid is also made air-tight by vase- 

 line. Piercing one side is a hole into which a tube fits tightly, and this 

 is connected by rubber tubing of small bore to a tambour (fig. 35). As the 

 kidney expands air is driven out of the plethysmograph into the tambour, the 

 lever of which therefore rises. 



DEMONSTRATION OF THE CHANGES IN VOLUME OF 

 THE KIDNEY" 



The apparatus is first set up as for taking a blood-pressure tracing, and a 

 tambour is also fitted up to record vertically above the blood-pressure tracing. 

 Care is taken that all the writing points record vertically above each other. 



A dog which has not been fed for the previous twelve hours is put under 

 ether and then a dose of morphia is injected, 1 c.c. of a 1 per cent, solution of 

 the hydrochlorate per kilo of body-weight. A median incision in the neck 

 is made, the external jugular isolated for about 1^ inches, and a simple cannula 

 inserted and tied in. The carotid artery is next exposed, and a cannula tied 

 in it as described on p. 170. The kidney is next exposed. This may be 

 done by a lateral incision in the lumbar region and the kidney isolated from 

 the peritoneum without opening the abdominal cavity if possible, though this 

 will be found of some difficulty in the dog. There are usually several small 

 vessels which enter directly into the cortex of the kidney. These have to be 

 divided ; but each must be ligatured before doing so in order to avoid hemor- 

 rhage into the oncometer. When the kidney is thoroughly freed it may be 

 placed in the oncometer. 



The other method, which has the great advantage that the kidney is more 

 fully exposed, is to reach it by opening the abdominal cavity from the front. 

 If care be taken to protect the exposed viscera from cooling, this method may 

 be safely adopted. A longitudinal median incision is made through the skin, 

 starting just below the xiphisternum for about three or four inches. A trans- 

 verse incision through the skin at the level of the last rib is now made, from 

 the mid-line down to the rib on the left side. The muscles are next cut 

 through, one at a time, along this line — first the external oblique, then the 

 internal oblique, then the transversalis, and finally the rectus. Care is taken 

 that the peritoneum is not opened until all bleeding has been stopped. As 

 each vessel is cut through it is caught up on Spencer Wells' forceps and 

 ligatured. When all bleeding has been arrested the abdominal cavity is 

 opened by cutting through the peritoneum along the incisions made through 

 the muscles and in the mid-line. The intestines are pulled well over to the 

 right side and protected by covering with a thick layer of cotton wool which 

 has been warmed in front of a fire. The kidney is then exposed and the 

 peritoneum over it is torn through, any bleeding point being ligatured. Care 

 is taken to handle the kidney as little as possible, and it must not be allowed to 

 become cooled. Having thoroughly isolated the kidney, especially where the 

 vessels leave it, it is placed in the oncometer. This has previously been pre- 

 pared by warming it and then placing a few layers of cotton wool containing 

 a plentiful amount of the vaseline and paraffin mixture at the bottom of the 

 notch in the side wall. The kidney is placed in the oncometer, so that the 

 vessels and ureter lie on the vaseline wool in the notch for that purpose. 

 Strips of wool soaked in the vaseline mixture are now packed, so as to lie 

 between the kidney and the notch, and others to fill up the notch. The whole 

 success of the experiment depends upon the careful packing at this stage. 

 The notch is to be exactly filled and not overfilled, so that when the lid is 

 adjusted there is no pressure on the kidney vessels. Before putting on the 

 lid the upper edge of the oncometer is thoroughly covered with vaseline 



