270 THE UR1SE. 



about 50 or 60 c.c., treated with ten times as much of 95 per cent, 

 alcohol, and set aside for twelve hours. It is then filtered and freed 

 from the alcohol by distillation. The residual fluid is acidified with 

 phosphoric acid, and repeatedly extracted with five times its volume 

 of ether. The ethereal extract is evaporated and the remaining 

 yellow syrup dissolved in a little water. Any hippuric acid which 

 may be present thus separates out and is filtered off. The filtrate is 

 now treated with pure lead carbonate in substance, heated on a 

 water-bath for thirty minutes, and filtered on cooling. From the 

 filtrate the lead is removed by means of hydrogen sulphide, and the 

 excess of the latter by gently warming on a water-bath. The 

 fluid is then concentrated to a thick syrup and extracted with ether. 

 The ethereal solution is evaporated and the residue boiled for some 

 time with water and an excess of zinc carbonate. The mixture 

 is filtered while hot, concentrated to a small volume, and then set 

 aside in the cold after adding a little alcohol. The zinc salts of 

 both paralactic acid and the common optically inactive lactic acid 

 which may also be present in traces, then crystallize out. They 

 can -be separated from each other by treating with absolute alcohol, 

 in which the latter is insoluble. It must be noted that the solu- 

 bility of the paralactate is also slight (1 : 1100), so that it is 

 necessary to add a large amount of alcohol. In order to prevent 

 confusion with the aromatic oxy-acids of the urine, the lactate 

 crystals should now be further identified, which is most conveniently 

 done by estimating the water of crystallization. The paralactate 

 contains two molecules of this, which escapes at 105 C., and at this 

 temperature the weight of the crystals should therefore diminish 12.9 

 per cent. The salt, moreover, like its acid, is laevorotatory, while 

 the common lactate is optically inactive. 



Leucin and Tyrosin. Leucin and tyrosin, according to some 

 observers, are normally present in the urine in traces. By others this 

 is denied, and I must admit that I have never found either of the 

 substances under normal conditions. In certain diseases of the 

 liver, however, in which extensive destruction of the hepatic cells 

 is going on, both may be found. But it is noteworthy that 

 while in acute yellow atrophy this is a common occurrence after 

 the first week of the disease, in acute phosphorus poisoning they 

 are usually not found. Thus far we have no adequate explana- 

 tion to offer for this difference, and we are in ignorance, more- 

 over, of the origin of the bodies in question in the former 

 disease. We have seen that as a general rule at least the greater 

 portion of the tissue nitrogen which is set free during the process 

 of metabolism is carried to the liver in the form of ammonium 

 paralactate, and there is no evidence to show that this may be 

 transformed into either leucin or tyrosin. We see, in fact, that in 

 extensive hepatic disease ammonium lactate appears in the urine. 

 Whether or not in acute yellow atrophy leucin and tyrosin are also 

 .set free in the tissues in general, we do not know. In the liver, it is 



