ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 325 



A careful comparison of the results obtained shows that Myxine bile, although 

 obviously differing in percentage composition, contains all the essential constituents of 

 ox bile, and hence the liver of Myxine is a true vertebrate liver, whatever else it may be. 



Both fluids have a greenish brown colour, but whilst ox bile is a clear viscous fluid, 

 Myxine bile is almost opaque. The latter, however, is of a much more watery con- 

 sistency, due to the presence of a smaller percentage of mucin. Myxine bile has the 

 characteristic bitter taste of ox bile, but the latter is more aromatic. Further, ox bile 

 is slightly alkaline to litmus paper, but Myxine bile is neutral. 



The presence of mucin and nucleo-protein may be tested for by adding a few drops 

 of acetic acid to a small quantity of bile, when a precipitate insoluble in excess of acid 

 is thrown down. Ox bile gave a bulky mucinoid precipitate with this test, but with 

 Myxine bile the precipitate was only sufficient to render the fluid turbid. With 

 methylated spirit both fluids gave a bulky precipitate of mucinoid nucleo-albumin 

 coloured by pigment. 



The pigment tests were not, on the whole, quite so pronounced as with ox bile, but 

 were sufficiently good to leave no doubt as to the presence of bile pigments in Myxine 

 gall. 



On shaking up a small quantity of ether with the two separate samples of bile, no 

 pigment was extracted by the ether, but, on the addition of a few drops of concentrated 

 hydrochloric acid, nucleo-protein was in both cases precipitated and pigment extracted 

 by the ether. Ox bile gave much the better result, both in the amount of the precipitate 

 and of the pigment extracted. Pigment was further tested for by Gmelin's ring test. 

 This is carried out by saturating a portion of filter paper with bile, and placing a drop 

 of fuming nitric acid in the centre of the saturated area. After a short time a number 

 of differently coloured concentric rings appear at the margin of the nitric acid drop, and 

 slowly spread. The order of the colours is (1) yellow, appearing at the junction of bile 

 and acid and due to the pigment choletelin ; (2) red ; (3) violet, passing into blue, due 

 to bilicyanin ; and (4) green, due to biliverdin. Owing to the limited quantity of 

 Myxine bile available, only a very small area of the filter paper could be saturated, but 

 rings of yellow, red, and blue could be faintly seen. Ox bile, again, gave the more 

 striking result. 



As regards bile salts Pettenkofer's test gave an excellent result with Myxine bile. 

 The test consists in adding a drop of 1 per cent, solution of cane sugar to a few drops 

 of bile, and thoroughly shaking. Concentrated sulphuric acid is then carefully poured 

 down the side of the tube, and at the junction of the two liquids a purple ring slowly 

 develops. On shaking, the contents of the tube are coloured a deep purple. By 

 using a solution of cane sugar and sulphuric acid only, by way of control, no purple 

 colour was produced, but only the characteristic brown colour due to the charring of 

 the sugar by the sulphuric acid. Hay's test depends on the presence of bile salts 

 reducing the surface tension of that liquid. When flowers of sulphur are placed on the 

 surface of bile they slowly sink to the bottom, but with water only the surface tension 



TRANS. ROY. SOC. EDIN., VOL. XLIX. PART II. (NO. 3). 42 



