CHEMICAL BASIS OF THE ANIMAL BODY. 227 



Spectrophotometers are instruments by which the value of I' (see above) and 

 hence of E may be determined. Those of Vierordt l and Hiifner 2 have been most 

 generally used for physiological purposes, but there are many other forms 3 . The 

 value of A has been determined by several observers for haemoglobin 4 , oxy-haemo- 

 globin 5 , carbon-monoxide hemoglobin 6 and methaemoglobin 7 , for certain fixed 

 parts of the spectrum ; as also its value for bile and urinary pigments 8 . If the 

 value of A has been determined for two substances in two different parts of the 

 spectrum the amount of each substance in a mixture of the two may be determined 

 spectrophotometrically 9 . This is a possibility of considerable importance when 

 working with blood in which varying amounts of haemoglobin and oxy-hasmoglobin 

 may occur simultaneously. 



6. Methaemoglobin. When blood or solutions of haemoglobin 

 which have been exposed to the air for some time are examined with 

 the spectroscope they are frequently found to exhibit, in addition to 

 the more or less persistent absorption bands of oxy-hsemoglobin, a 

 marked band of absorption between C and Z>, closely resembling but 

 differing slightly in position from the band which haematin shows in acid 

 solution (see below). This band may also frequently be observed in many 

 pathological fluids, such as those from ovarial cysts etc., which are 

 coloured by blood, and in urine when similarly coloured 10 . The sub- 

 stance to which the band is due is known as methaemoglobin 11 . It may 

 be readily prepared in the laboratory by the action of many reagents 

 such as acids or alkalis, or more conveniently of certain salts, on solutions 

 of oxy-haemoglobin. Of these salts those which may perhaps on the 

 whole be most advantageously employed to obtain the spectrum of 

 met haemoglobin are nitrites 12 , potassium ferricyanide, or potassium 

 permanganate 13 . With the two latter salts the spectrum of methaemo- 

 globin may be obtained as follows. To 10 c.c. of a moderately strong 



1 loc. cit. (i), S. 52. 



2 Jn. f. prakt. Chem. N.F. Bd. xvi. (1877), S. 290. Cf. Otto, Pfliiger's Arch. 

 Bd. xxxvi. (1885), S. 12. Glazebrook has constructed a modification of Hiifner's 

 instrument. See Lea, Jl. of Physiol. Vol. v. (1883), p. 239. 



3 For all details of instruments and spectrophotometry in general see G. u. H. 

 Krliss, Kolorim. u. quant. Spektralanal. 1891. Very complete details are given in 

 Neubauer u. Vogel, Analyse d. Harns, 1891, S. 411. 



4 Hiifner, Zt.f. physiol. Chem. Bd. in. (1879), S. 7. 



5 Hiifner, Ibid. Bde. i. (1878), S. 317, in. (1879), S. 4. Von Noorden, Ibid. 

 Bd. iv. S. 9. Otto, Ibid. Bd. vn. S. 62. Pfliiger's Arch. Bd. xxxi. (1883), S. 244. 

 xxxvi. (1885), S. 12. Sczelkow, Ibid. Bd. XLI. (1887), S. 373. 



6 Marshall, Zt. f. plnjsiol. Chem. Bd. vn. (1882), S. 81. 



7 Otto, Pfliiger's Arch. Bd. xxxi. (1883), S. 263. 



8 See Vierordt, loc. cit. or G. u. H. Kriiss, loc. cit. 



9 Vierordt, loc. cit. 



10 Hoppe-Seyler, Zt. f. physiol. Chem. Bd. v. (1881), S. 6. 



11 The name was first used by Hoppe-Seyler in 1865, Centralb. f. d. med. Wiss. 

 S. 65. But see also previously Ibid. 1864, S. 834 and Virchow's Arch. Bd. xxix. 

 (1864), Sn. 233, u. 597. 



12 Gamgee, Phil. Trans. 1868, p. 589. 



13 Jaderholm, Zt. of Biol. Bd. xm. (1877), S. 193. 



