274 Proceedings of the Royal Irish Academy. 



the degree pitched upon was 51°, and the Frauenhofer a well-known 

 line between F and G, which I designate (little) g. Having now 

 either fixed the instrument permanently to the bench, or else very 

 accurately marked out its position, a permanent working constant is 

 established ; for when the instrument is in its exact place, and the 

 zero rests on the selected degree, the observer may be sure (even 

 when working by artificial light) that the needle points to the 

 position corresponding to g. Should the observer be working in a 

 strange place, and without sunlight, there is a bright potassum line 

 on the violet side of g, which will give an equally good constant, and 

 may even be made by a previous observation to determine g. The 

 total range of the spectrum of my testing instrument from g in the violet 

 to B in the red is 3° 38' ; of which average human bile absorbs 2° 23', 

 leaving 1° 15' (or a small fraction more than one-third) of the spectrum 

 unaffected. In human bile the golden red colouring matter, known 

 as Bilirubin deHigNoOs predominates ; but in that of the ox and sheep 

 the green Biliverdin [C16H20N2O5, ox according to Maly 0161118^204] 

 is in the ascendant, sheep bile being the greener of the two. It is 

 therefore interesting to find that the absorptive co-efficients of these 

 biles exhibit corresponding differences — that of the ox absorbing 2° 1 3', 

 and that of the sheep 2° 7', as compared with the 2° 23' of human 

 bile. I now proceeded to examine the effect of aqueous solutions of 

 bile of gradually increasing strength ; and for this purpose, on account 

 of the difficulty of obtaining perfectly fresh human bile in quantity, 

 used fresh ox bile. The weakest solution which produced any per- 

 fectly definitive effect on my instrument was 5 per cent. ; which was 

 of a very pale straw-colour, and exhibited an absorption of 6'. Sub- 

 mitting solutions of gradually increasing strength and colour, I found 

 that there was an increase of about 8' for every 5 per cent, of bile up 

 to 75 per cent., when the solution scarcely differed in appearance or 

 opacity from pure bile, and produced an absorption of only 20' less 

 than that of the pure secretion (2° 13'). The shadow thus produced 

 was of an olive greenish black, greener than that of blood (which I 

 shall presently describe) ; different from any other shadow that I am 

 acquainted with; and, in my experience, pathognomonic of the colouring 

 matter of bile. And I may add that, in many instances, the daily 

 observations of the increase or decrease of bile colouring matter, so 

 made, has been most useful for diagnostic purposes. The cardinal 

 point, however, connected with this test is, that bile, from its weakest 

 Bolution up to absolute purity, does not exhibit any separate absorp- 

 tive bands or touch the red end of the spectrum ; and the importance 

 of this point I will presently explain. 



To establish the value of the test, however, it is essential to inquire 

 whether any of the normal or abnormal constituents of the urine, ex- 

 cept bile, possesses this special absorptive power. I have searched 

 long and carefully into this question, but with a negative result. 

 Commencing with the colloids, albumen has no effect upon the spec- 

 trum, nor have pus or mucus. Blood is frequently found, as a 



