128 



THE MICROSCOPE. 



changing tlie cell held on the eye-piece for a tube con- 

 taining an ammoniacal solution of cochineal, it is easy to 

 show that, though it yields a spectrum with two absorp- 

 tion-bands, more like those due to blood than I have seen 

 in any other substance, they differ so much in relation, 

 size, and position, that there is no chance of their being 

 confounded when compared together side by side." ^ 



(1) We have been usually taught that the red-blood corpuscles consisted of 

 two substances, hEeraatin and globulin ; but later researches lead to the belief 

 that they consist of one crystalline substance, termed globulin or hccmato-glohu- 

 lln. A solution of this substance, as well as of certain products of its decom- 

 position, produces the absorption-bands referred to. Hoppe was the first to 

 demonstrate this fact : he found that a very dilute solution of blood was suffi- 

 cient for the purpose. Professor Stokes proved that this colouring-matter is 



capable of existing in two 



% 



No. 1. Arterial Blood, Scarlet Cruorine. 



No. 2. Venous Blood, Purple Cruorine. 



Blood treated with Acetic Acid. 



Solution of Hmmaiin. 



ABSORPTION-BANDS, AFTER STOKES. 



states of oxidation, and that 

 a very different spectrum 

 is produced according as 

 the substance, which he 

 has termed cruorine, is in 

 a more or less oxidised 

 condition.* Proto-sulphate 

 of iron, or proto-chloride 

 of tin, causes the reduction 

 of the colouring-matter, 

 and, by exposure to air, 

 o.xygen is absorbed, and 

 the solution again exhibits 

 the spectrum character- 

 istic of the more oxidised 

 state. The different sub- 

 stances obtained from 

 blood colouring - matter 

 produce different bands. 

 Thus, hcematiii gives rise 

 to a band in the red spec- 

 trum ; hcemato - globulin 

 liroduces two bands, the 

 second twice the breadth 

 of the first in the yellow 

 portion of the spectrum 

 between the lines d and i^, 

 No, 1. The absorption- 

 bands differ according to 

 the strength of the solu- 

 tion employed, and the 

 medium in which the blood- 

 salt is dissolved ; but an 

 exceedingly miimte pro- 

 portion dissolved in water 

 is sufficient to bring out 

 very distinct bands 



* Professor Stokes, "On the Reduction and Oxidation of the Colouring- 

 matter of the Blood" (Proceed. Royal Sac. vol. xiii. p. 355). The oxidising 

 solution is made as follows : — To a solution of proto-sulphate of iron, enough 

 tartaric acid is added to prevent precipitation by alkalies. A small quantity of 

 this solution, made slightly alkaline by ammonia or carbonate of soda, is to be 

 added to the weak solution of blood in water. 



