of the Fishery Board for Scotland. 



175 



Tetronerythrin, the red pigment. — In addition to the blue colour, there 

 is also in solution in the blood plasma a small amount of a red pigment. 

 In most specimens of fresh-water crayfishes, lobsters, and crabs, it is 

 present in large quantities. The fact of its occurrence in the lobster is 

 mentioned by Fredericq. In its identification I have received many 

 valuable suggestions from Dr M'Munn of Wolverhampton. It is not a 

 proteid, being readily extracted from the blood by means of alcohol. It 

 belongs to the class of pigments known as luteins or lipochromes, and 

 gives all the tests that Capranica and Schwalbe describe as characteristic 

 of those bodies, viz. : — 



1. It is soluble in alcohol, ether, chloroform, benzol, turpentine, 



bisulphide of carbon, and slightly in olive oil. 



2. With sulphuric acid it gives a violet colour. 



3. With nitric acid, an evanescent bluish green colour. 



4. With iodine dissolved in solution of iodide of potassium, a violet 



colour. This test is only obtained readily after the saponifica- 

 tion of the pigment by the addition of strong caustic soda to 

 the alcoholic solution. 



It is the same pigment that occurs in the shell of the animal, and which 

 has received the name of tetronerythrin. Dr M'Munn has shown that it 

 is probably formed in the liver of the Crustacea; and on comparing spectro- 

 scopically the pigment taken from these three situations — the exoskeleton, 

 the blood, and the hypoderm — they are seen to be identical. There is a 

 small cutting off of the red end of the spectrum, and the blue end is cut 

 off up to the E line, or a little on the red side of it. In a more dilute 

 solution less of the red end is cut off, and a band in the region of the F 

 line becomes detached from the large absorption of the blue end. This is 

 not a very dark band, and in very dilute solutions appears only as an ill- 

 defined shading. 



It is a pigment that occurs pretty widely distributed in the animal 

 kingdom. Merejkowski found it in 104 species of animals, vertebrate 

 and invertebrate (Comptes rendnes, tome xciii. p. 1029, 1881). He sup- 

 poses it to have an important action in cutaneous respirations, on account 

 of the large quantity in which it occurs in the gills. Oxidation and 

 ^•eduction produce, however, no effect on it when separated out from the 

 parts in which it occurs. It becomes colourless when exposed for some 

 time to the air, but this discolouration occurs equally well in a vacuum. 



Its presence in the blood is interesting, as showing how it passes from 

 the liver, where it is probably formed, to tlie surface, where it is probably 

 used for respiratory or other purposes. Seeing how abundant this pigment 

 is in the shell of nephrops, it is difficult to account for the small quanti- 

 ties in which it occurs in the blood. There are, however, many lobsters 

 in the blood of which it occurs in equally small quantities. In these, as 

 in many specimens of nephrops' blood, I at first thought it was absent ; 

 the alcoholic extract is colourless ; still, on evaporating it down to a small 

 bulk, it becomes of a faint orange red colour ; and, later still, flakes of the 

 pigment separate out. 



General Conclusions. 



The chief results of this investigation of the physiological and chemical 

 properties of the blood of nephrops norwegicus may be summarised as 

 follows : — ' 



