108 A CYTOLOGICAL STUDY OF THE KIDNEY CELL 



was no limitation of water intake, except that with the idea of straining the urea- 

 concentrating capacity of the kidney, we removed the water tube from the cage of 

 the urea-fed rats for one hour each day following the giving of fresh food. 



There can be no doubt that by these measures we succeeded in making the 

 kidneys of the urea-fed group do much more work than those of the controls. In 

 spite of repeated efforts, however, we cannot give any accurate measure of the 

 difference, since we did not succeed in entirely overcoming the technical difficulties 

 of collecting urine from such small animals. We did find, however, that the urea- 

 fed rats took about twice as much water and excreted about twice as much urine. 

 This urine at times contained as much as 10 per cent of urea. The funnel over 

 which the urine ran into the collecting vessel was usually coated with urea crystals. 

 Examination of the feces showed that urea was not excreted by the gastro- 

 intestinal tract. 



At the end of sixteen months various accidents had reduced the number of 

 rats to eight, four controls and four urea-fed. After a functional test, which will 

 be described below, these rats were killed by bleeding from the carotid artery after 

 very short ether anaesthesia, and the kidneys at once removed and weighed. The 

 results are given in Table I. They fail to show the existence of any hypertrophy. 



TABLE I 

 KIDNEY WEIGHTS OF CONTROL AND UREA-FED RATS 



Controls 



Kidney Weight as a 

 Percentage of Body 

 No. Kidney Weight Body Weight-Alimentary Tract Weight- Alimentary Tract 



1 

 2 

 3 

 4 



No. 



On the day before each animal was killed an attempt was made to measure 

 the urea-excreting capacity of the kidneys. In order that both groups might be 

 under the same conditions, no urea was given to the urea group for two days 

 before the experiment. Urea in concentrated solution, 0.5 gms. for one pair of 

 rats, and 0.375 for the other three pairs, was injected from a syringe through a 

 fine tube into the stomach. The rat was then placed over a funnel, so that all 

 urine was collected. After three hours the carotids were cut under ether anaes- 

 thesia, and the blood collected. The urea content of both blood and urine was 

 determined by the usual urease aeration method. The results are given in Table II. 



