N URINE. 249 



waste of the tissues or by an obstruction of the organs con- 

 ig oxygen, as the lungs and skin, or, as is probably the 

 case in the majority of instances, by an excess of food being 

 taken over and above the requirements of the system. As 

 regards the constitution of this body, I think there can be no 

 doubt that it contains the elements of indigo-blue and sugar, 

 and that by oxidation within the system it is converted into 

 the ordinary extractive matter of urine, which contains, as I 

 have ascertained, the elements of sugar and of the black sub- 

 stance which is formed by the action of strong acids on urine, 

 and which may be considered as a product of the oxidation of 

 indigo-blue. Having prepared the extractive matter of urine 

 in a state of purity, ascertained its composition, and examined 

 its products of decomposition, I think it is probable that the 

 indigo-producing body will be found, as regards its formation 

 and composition, to occupy a place between the substance of 

 the tissues and the ordinary extractive matter of urine. The 

 very minute quantities of it ordinarily occurring in urine, and 

 the difficulty of separating it from the extractive matter, make 

 it, however, impossible to ascertain whether this is the case or 

 not. My object in making known this portion of the inves- 

 tigation in its present fragmentary state, is to induce medical 

 men, who have an opportunity of examining many varieties 

 of urine, to endeavour to discover among these varieties some 

 containing a sufficiently large quantity of this body to enable 

 the chemist to ascertain its properties and composition. 



The formation of a substance containing the elements of 

 indigo-blue in the animal system is a fact which may lead to 

 important conclusions regarding the chemical composition of 

 the complex bodies of which the blood and tissues consist. 



2K 



