PHYSIOLOGY OF THE LIVER AND SPLEEN. 759 



if ammonium carbonate was added to the blood circulating through 

 the liver to that from the fasting as well as from the well-nourished 

 animal a very decided increase in the urea was always obtained. 

 It follows from the last experiment that the liver cells are able to 

 convert carbonate of ammonium into urea. The reaction may be 

 expressed by the equation (NH 4 ) 2 CO 3 -2H 2 O = CON 2 H 4 . Schon- 

 dorff * in some later work showed that if the blood of a fasting dog 

 is irrigated through the ru'nd legs of a well-nourished animal, no 

 increase in urea in the blood can be detected; but if the blood, after 

 irrigation through the hind legs, is subsequently passed through the 

 liver, a marked increase in urea results. Obviously, the blood in this 

 experiment derives something from the tissues of the leg which the 

 tissues themselves cannot convert to urea, but which the liver cells 

 can. Finally, in some remarkable experiments upon dogs made by 

 four investigators (Hahn, Massen, Nencki, and Pawlow), which are 

 described more fully in the next chapter, it was shown that when the 

 liver is practically destroyed there is a distinct diminution in the 

 urea of the urine. In birds uric acid takes the place of urea as the 

 main nitrogenous excretion of the body, and Minkowski has shown 

 that in them removal of the liver is followed by an important 

 diminution in the amount of uric acid excreted. From experiments 

 such as these it is safe to conclude that urea is formed in the liver 

 and is then given to the blood and excreted by the kidney. In 

 treating of the physiological history of urea an account will be given 

 of the views proposed with regard to the antecedent substance or 

 substances from which the liver produces urea. 



Physiology of the Spleen. Much has been said and written 

 about the spleen, but we are yet in the dark as to the distinctive 

 function or functions of this organ. The few facts that are known 

 may be stated briefly without going into the details of theories that 

 have been offered at one time or another. The older experimenters 

 demonstrated that this organ may be removed from the body without 

 serious injury to the animal. An increase in the size of the lymph- 

 glands and of the bone-marrow has been stated to occur after ex- 

 tirpation; but this is denied by others, and, whether true or not, it 

 gives but little clue to the normal functions of the spleen. Some 

 observers f find that the removal of the spleen causes a marked 

 diminution in the number of red corpuscles and the quantity of 

 hemoglobin. They infer, therefore, that the spleen is normally 

 concerned in some way in the formation of red corpuscles. Others, 

 however, report with equal positiveness that removal of the spleen 

 has no effect upon the number of red corpuscles or upon the power of 

 the animal to regenerate its corpuscles after hemorrhage. { The 



