128 



THE MICROSCOPE. 



changing the 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." l 



We have been usually taught that the red-blood corpuscles consisted of two 

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

 that they consist of one crystalline substance, termed globulin or hcemato-globu- 

 lin. 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 

 statesofoxidation,andthat 

 a very different spectrum 

 is produced according as 

 the substance, which hrf 

 has termed cruorine, is in 

 a more or less oxidised 

 condition. 2 Proto-sulphate 

 of iron, or proto-chloride 

 of tin, causes the reduction 

 of the colouring-matter, 

 and, by exposure to air, 

 oxygen 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. 



I 111 9B'] IIBH1 HHilHHH Thus, hmnatin gives rise 

 to a band in the red spec- 

 tram ; hcemato - globulin 

 I produces two bands, the 

 second twice the breadth 

 of the first in the yellow 

 portion of the spectrum 

 between the lines D and E, 

 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 minute pro- 

 portion dissolved in water 

 is sufficient to bring out 

 very distinct bands. 



No. 1. Arterial Blood, Scarlet Cruorine. 



No. 2. Venous Blood, Purple Cruorine. 



No. 3. Blood treated with Acetic Acid. 



II 



No. 4. Solution of Hcematin. 



ABSORPTION-BANDS, AFTER STOKES. 



(1) Popular Science Review, January, 1866. 



(2) Professor Stokes, " On the Reduction and Oxidation of the Colouring- 

 matter of the Blood" (Proceed. Royal Soc. 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. 



