178 Br Latham, On the Conversion of [Feb. G, 



its product leucin, and its companion tyrosin ; but if, especially 

 when a meal rich in proteids has been taken, a considerable 

 quantity of leucin is formed, we can perceive an easy and direct 

 source of urea, provided that the metabolism of the body is 

 capable of converting leucin into urea. That the body can effect 

 this change is shewn by the fact that leucin, when introduced into 

 the alimentary canal in even large quantities, does reappear in the 

 urine as urea ; that is, the urine contains no leucin, but its urea is 

 proportionately increased ; and the same is probably the case with 

 tyrosin. Now the leucin formed in the alimentary canal is carried 

 by the portal blood straight to the liver ; and the liver, unlike 

 other glandular organs, does, even in a perfectly normal state of 

 things, contain urea. We are thus led to the view that among 

 the numerous metabolic events which occur in the hepatic cells, 

 the formation of urea out of leucin or out of other antecedents 

 may be ranked as one. Probable, however, as this view may 

 seem, it has not as yet been established as a fact." 



" The view that leucin is transformed into urea lands us, how- 

 ever, in very considerable difficulties. Leucin, as we know, is 

 amido-caproic acid ; and, with our present chemical knowledge, we 

 can conceive of no other way in which leucin can be converted into 

 urea than by the complete reduction of the former to the ammonia 

 condition, and a reconstruction of the latter out of the ammonia 

 so formed. We have a somewhat parallel case in glycocoll (or 

 glycocine). This, which is amido-acetic acid, when introduced 

 into the alimentary canal also reappears as urea; here too, a 

 reconstruction of urea out of an ammonia phase must take place*." 



Again, 



" To ascertain the influence of the liver in the formation of 

 urea, Solnikoff has established a direct connexion between the 

 portal and jugular veins by means of an india-rubber tube, an 

 operation which, if carefully performed, is borne with impunity. 

 Vascular pressure at first lowered, soon returns to the normal. 

 The urinary secretion was, however, completely arrested, and was 

 not re-established until urea had been injected into the veins of 

 the animal. The only effect of these injections was to raise the 

 vascular pressure. The results were in no way modified by the 

 preceding section of the splanchnic nerves. If on the other hand, 

 instead of the portal, the crural vein is placed in communication 

 with the jugular vein, the urinary secretion is unchanged. It is 

 thus clear that the urea which passes out of the system by the 

 kidneys, enters the circulation with the blood which issues from 

 the liver-f-." 



* Foster's Physiology. 3rd Ed. pp. 1U4, i05. 

 t Lancet, Dec. 3, 1881, p. 971. 



