74 



Mr. E. Scliunck on the Colouring and 



[Recess^ 



conferred. With some cliemists, to call a body an extractive matter is to 

 place it among a class which is held to be unworthy of minute examina- 

 tion. To others the name extractive matter is merely a convenient word 

 for a mixture, sometimes occurring in nature, of certain definite, perhaps 

 even crystallized substances, which, by appropriate means, may be resolved 

 into its constituents, and thus be made to disappear entirely from the list 

 of definite chemical bodies. As regards the extractive matter of urine, this 

 view may to some extent be justified, when we recollect that from what 

 was considered to be extractive matter sixty years ago, such well- character- 

 ized substances as urea, hippuric acid, and creatine have been successively 

 eliminated ; and it is therefore natural to expect that by further research 

 it will be found to contain others of the same nature. I believe this view 

 to be erroneous ; and I shall succeed, I hope, in showing that, after having 

 removed from the extractive matter of urine everything which can assume 

 a definite form, there remains a residuum which cannot be further resolved 

 without decomposition. Still, any one holding this view is not likely to 

 undertake the investigation of extractive matters as such, unless it be for 

 the purpose of obtaining something which may be supposed to be contained 

 in them. Lastly, the properties of these colouring and extractive matters, 

 however important they may be to the physiologist and pathologist, pre- 

 sent so little that is interesting to the chemist, that the latter would pro- 

 bably not occupy himself with their examination unless for some particular 

 purpose. For myself, I frankly confess that, had I not had a special 

 object in view, this investigation would not have been undertaken. The 

 information for the sake of which it was commenced having been obtained, 

 I should then have abandoned all further inquiry, had I not found 

 reason to suppose, in the course of my experiments, that a more extended 

 investigation would lead to results interesting from a physiological point of 

 view. My endeavours have, I think, been attended with some measure of 

 success ; and should physiologists, on becoming acquainted with the results, 

 be of the same opinion, my labour will not have been quite in viiin. 



The colouring-matters which occurr in, or have been obtained from, 

 urine may be divided into three classes, viz. : — - 



1st. Those which are only found occasionally in it, in consequence 

 either of disease or of some abnormal state of the system. 



2ndly. Those which are produced by spontaneous decomposition, or by 

 the action of reagents on substances, either coloured or colourless, pre- 

 existing in the urine. 



Srdly. The colouring- matter or matters occurring in normal urine, and 

 to which its usual colour is due. 



A few remarks on the present state of our knowledge on these three 

 classes of pigments, as derived from the labours of my predecessors as well 

 as my own, may not be out of place. 



I. The abnormal colouring-matters, which are found ready formed in 

 the urine, may either be peculiar to the secretion, or their presence may be 



