406 EXCRETION". 



including every thing but the ureter. The ligature was then loosened, so as to admit the 

 blood, but the nerves had been bruised and destroyed. The secretion of urine continues, 

 however, under these circumstances, for only a few hours. It then ceases, and the nutri- 

 tion of the kidney becomes profoundly affected, its tissue breaking down into a putrid, 

 semifluid mass, which probably enters the blood and is the cause of death. 



The other physiological conditions that affect the urinary excretion influence the com- 

 position of the urine and the quantity of excrementitious matters separated by the kid- 

 neys. These will be more appropriately considered under the head of nutrition and dis- 

 assimilation. It is sufficient to remark, in this connection, that, during digestion, when 

 the composition of the blood is modified by the absorption of nutritive matters, the quan- 

 tity of urine is usually increased. This is particularly marked when a large amount of 

 liquid has been taken. 



As the excrementitious principles eliminated by the kidneys are being constantly pro- 

 duced in the tissues by the process of disassimilation, the formation of urine is constant ; 

 presenting, in this regard, a marked contrast with the intermittent flow of most of the 

 secretions proper, as distinguished from the excretions. It was noted by Erichsen, in a 

 case of extroversion of the bladder, and it has been farther shown by experiments upon 

 dogs, that there is an alternation in the action of the kidneys upon the two sides. Ber- 

 nard exposed the ureters in a living animal and fixed a small silver tube in each, so that 

 the secretion from each kidney could be readily observed ; and he noted that a large 

 quantity of fluid was discharged from one side for from fifteen to thirty minutes, while 

 the flow from the other side was slight and in some instances was entirely arrested. The 

 flow then commenced with activity upon the other side, while the discharge from the 

 opposite ureter was diminished or arrested. We are already familiar with this alterna- 

 tion of action in the parotid glands. 



Changes in the Composition of the Blood in passing through the Kidneys. Some of 

 the changes in the blood in its passage through the kidneys have already been noted. 

 The most important of these consist in a diminution in the proportion of urea, the urates, 

 and other of the excrementitious principles found in the urine. This would be expected, 

 inasmuch as these principles are constantly present in the urine, and they have been shown 

 to be derived exclusively from the blood. It has been ascertained, also, that the blood 

 of the renal veins contains less water than the blood of any other part of the venous sys- 

 tem. The constant separation of water from the blood by the kidneys, for the purpose 

 of carrying off the soluble excrementitious principles, is an explanation of this fact. It 

 was also observed by Simon, a number of years ago, that the blood of the renal veins 

 does not coagulate readily, and that it is impossible to obtain fibrin from it in the ordinary 

 way by stirring with rods. 



Reference has already been made to the researches of Bernard, showing that the 

 blood coming from many of the glands during their functional activity is but little dark- 

 er than arterial blood. The action of the kidneys is constant, and the quantity of blood 

 which they receive is enormous. Unless the function of these organs be disturbed, the 

 blood passing through them cannot be deoxygenated, and it is consequently red, contain- 

 ing a large quantity of oxygen and a very small proportion of carbonic acid. This fact 

 we have often noted, and it has been observed by all who have examined the renal veins 

 in living animals. In comparative analyses for gases of the blood of the renal artery and 

 vein, Bernard found, in one examination, no carbonic acid in either specimen, the pro- 

 portion of oxygen being 12 parts per hundred in volume for the artery, and 10 parts 

 for the vein. These observations were made at a temperature of from 50 to 53 Fahr. 

 Making the analyses at about the temperature of the body (104 to 113), the quantity 

 of carbonic acid was 3 parts for the artery and 3*13 parts for the vein, and the propor- 

 tion of oxygen was 19-46 parts for the artery and 17*26 parts for the vein. When the 

 secretion of urine was arrested by irritation of the kidney, the blood became black in 



