SPECIFIC OXYGEN CAPACITY 61 



in the bloods which were investigated by Peters, though it may- 

 have been present to the extent of 1 or 2 per cent, of the whole 

 haemoglobin analysed; these experiments, however, only covered a 

 very limited range of the animal kingdom and took no account of 

 pathological cases. Curious things can occur. I once killed a rat 

 which had brown blood, yet a casual observation with the spectro- 

 scope failed to reveal the cause. 



Recent research has revealed another substance — is it another 

 substance? or is it the same under another name? — that substance 

 is variously called kathaemoglobin or parahaematin. It was described 

 by Arnold (23) and v. Klaveren(24), and has been investigated recently 

 by Keilin(25). Briefly, when haemochromogen is oxidised within very 

 narrow limits of hydrogen-ion concentration, near neutrality, para- 

 haematin is formed. The protein does not split off from the haematin, 

 as according to them it does if the solution is alkaline, but remains 

 attached to it. The result is a substance possessing a spectrum which 

 bears a superficial resemblance to oxyhaemoglobin, but which does 

 not yield up its oxygen to potassium ferricyanide or to a vacuum. 

 Whether parahaematin and inactive haemoglobin are the same thing, 

 or are different things, remains to be seen. If, however, Peters' 

 estimate of the specific oxygen capacity of haemoglobin was 2 per 

 cent, too low the presence of parahaematin must be included among 

 the possible causes. 



In no case, however, is there reason to doubt that the iron and the 

 oxygen in haemoglobin are united in the proportions of two atoms 

 of detachable oxygen to one of iron. 



REFERENCES 



(1) Bayliss. Principles of General Physiology, ch&p. Tixi. 2nd ed. 1918. 



(2) Anson and Mirsky. Journ. Physiol, lx. 50. 1925. 



(3) Bohr. Skand. Arch. f. Physiol, ui. 101. 1892. 



(4) ToBiESEN. Skand. Arch. f. Physiol. \l. 273. 1895. 



(5) Abrahamsen. Vber den Sauerstojf des Blutes, 47. Kopenhagen, 1893. 



(6) Bohr. For a full discussion vide Nagel's Handbuch, i. 93. 1909. 



(7) BoRNSTEiN and Muller. Arch. f. Anat. u. Physiol, p. 470. 1907. 



(8) Masing AND SiEBECK. Deut. Arch. fuT Klin. Med. xcvui. 123. 1909; xcix. 130. 



1910. 



(9) BiTTTERFiELD. Zeitsch. Physiol. Chem. xlii. 143. 1909. 



(10) Bohr. Skand. Arch. f. Physiol, m. 76. 1892. 



(11) Peters. Journ. Physiol, xliv. 131. 1912. 



