UuiNLAN — On S^Jeetroscopic Estimation of Bile. 273 



certain essential oils. It will thus be seen that a simple and reliable 

 test of the colouring matter of bile is a desideratum ; and the one I 

 propose is founded on the fact that this colouring matter possesses a 

 power of selective absorption of the solar spectrum, commencing with 

 the violet, and extending (according to the quantity present) nearly 

 as far as Frauenhofer line D. Further, that this colouring matter 

 does not produce any absorptive bands, nor interfere with the red end 

 of the spectrum. After many trials I found that this test is best em- 

 ployed by placing in front of the slit a stratum of fluid of ^mm. in thick- 

 ness ; a thinner one has not sufficient absorptive power, and a thicker 

 is not so delicate — a very deep stratum (even though the solution be 

 weak as regards bile) produces a coarse obscuration not suitable for the 

 test. So many skilled observers are now employed in every branch of 

 medical research, especially in Germany, that it is not impossible that 

 this test may have been already described by somebody else. I do not, 

 however, see any mention of it in Neubauer and Vogel on the Urine, 

 or in Frerichs on the Liver ; and the exhaustive and admirable work 

 on Physical Diagnosis of Guttmann of Berlin, just issued by the Syden- 

 ham Society, is equally silent. I first observed it some years ago 

 when examining jaundiced urine with a small spectroscope, exhibiting 

 two conterminous and independent spectra lighted from different 

 sources ; and I found the test so useful for clinical teaching purposes, 

 that I procured a larger instrument specially adapted for its develop- 

 ment. In fact, with a Jellett saccharimeter and this instrument a 

 clinical teacher is able to test most delicately for albumen, diabetic 

 sugar or bile, and to estimate the two former exactly, and the latter 

 approximately — and all this with much less trouble and less loss of time 

 than in the ordinary coarse clinical procedures. Returning to the 

 bile test, I wish to mention that it is not my intention on the present 

 occasion to discuss its medical value — a subject more congenial to a 

 purely medical society. For the present I will assume that it is im- 

 portant to the physician to be able to detect bile in the urine in jaun- 

 diced patients, and to watch its increase or decrease ; and, having 

 made this assumption, will describe the details of the test, and respect- 

 fully invite the opinion of this eminent scientific body on its strictly 

 scientific aspect. The instrument is a single prism one, the telescope 

 of which is furnished with a fine needle^ in the eye-piece, and revolves 

 (with a coarse and fine adjustment) on a segment of the ordinary 

 <legree circle — the collimating tube having before the slit a means of 

 liolding a thin, flat glass test-tube of 2nvm. in thickness. Minutes as 

 well as degrees can be read off by the aid of an ordinary vernier. I 

 place this instrument on my laboratory bench, in front of a window, 

 in such a manner that, while the needle is resting on some definite 

 Frauenhofer line, as far back in the violet as possible, the zero of 

 the vernier may point exactly to some degree. In the present instance 



2 This needle was first suggested by Professor O'Eeilly, M.R.I.A.. of the College 

 of Science, DubKn ; and is, in my opinion, superior to any of the usual means of 

 spectrum measurement. 



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