PHYSIOLOGY OF THE INVERTEBRATA. 151 



part due to the oxidation of a chromogen, if so we may infer 

 tlie existence of such, and name it echinochromogen. 



Echinochrome differs from the blood pigments of most 

 Invertebrates, as it is readily dissolved by a great number of 

 solvents. 



It can be obtained in solution and isolated by two 

 methods : — "(a) The fresh blood-clot can be extracted with the 

 solvents mentioned before, or (&) tbe clot may be separated 

 from the serum by filtering, the pigment dried at the tempera- 

 ture of the air (as it changes by using heat) and the dried 

 pigment thus obtained treated by solvents. By the adoption 

 of the latter method it can be obtained in a purer condition." 



" The ' serum ' after separation of the clot is a faint yellow 

 colour and shows two faint bands in the green, but if allowed 

 to stand some time in contact with the clot it becomes a 

 faint violet red," and then gives the spectrum seen in Pig. 

 29, 6. On the addition of stannous chloride to the serum 

 dark bands (Fig. 29, c) make their appearance. These bands 

 have the following positions, \ S41.S to X 532 and X 506 to 

 X 486.5. In the oxidised condition the serum has a spectrum 

 of the same kind but the bands are feebler. The serum 

 is " faintly acid or neutral, faintly opalescent on heating, 

 opalescent with absolute alcohol, and faintly so with ether." 



Spectra Fig. 29, d and e are those of the brownish-red 

 clot, after standing in contact with the serum and with sodium 

 hydroxide respectively. 



The red alcoholic solution of the clot gives the spectrum 

 represented in Fig. 29,/. These bands read: first, X 557 to 

 X 545.5 ; second, X 524.5 to X 501 ; third, X494.S to X475. 

 On the addition of ammonium sulphide two new bands make 

 their appearance. The first is from X 531 to X 507 ; and the 

 second, X494.S to X475, the colour of this solution being 

 changed to yellow, and on shaking with air remained the same. 



On the addition of acetic acid to an alcoholic solution of 

 the fresh clot, the spectrum given in Fig. 29,^ is seen. " The 

 spectrum of the original absolute alcohol solution is that 



