72 Chapter V 



temperature, that is so much to the good, but the temperature of 

 the body is roughly speaking the same throughout. It has to suit 

 itself to a thousand reactions. But in virtue of the fact that the 

 haematin is allied to a protein the rate of reaction is influenced by 

 the degree of aggregation of the protein elements, and this may 

 "vary" with the concentration and nature of the electrolytes in 

 which they are placed and these electrolytes may differ from place 

 to place according as is most suitable for the chemical actions which 

 depend upon them. The same considerations may be applied to 

 the local effects of acids and alkalis. Here then is a possible basis 

 for biochemical "variation." The dog has salts of one type in his 

 corpuscle, the pig salts of another ; the dog's oxyhaemoglobin breaks 

 up therefore at one velocity, the pig's at another. This is no doubt 

 as much a matter of natural selection as are the morphological features 

 of the animals in question. But what is true of the reaction haemo- 

 globin is probably true of those of other colloids ; we recognise it in 

 the case of haemoglobin because haemoglobin has a simple reaction 

 with oxygen which we can investigate. 



But I must cease from speculating and turn to the next portion 

 of my subject, namely the consideration of haemoglobin as a vehicle 

 for the transport of oxygen in the body. 



REFERENCES 



(1) Bohr, Hasselbalch and Krogh, Skand. Arch.f. Physiol. xvi, p. 390, 1907. 



(2) Barcroft and Orbeli, Journal of Physiol. XLI, p. 353, 1910 ; Barcroft, Ibid. 



XLII, p. 44, 1911. 



(3) Mathison, Ibid. XLIII, p. 347, 1911. 



(4) Hasselbalch, Skand. Arch, xxvn, p. 13, 1912. 



(5) Douglas, Haldane and Haldane, Journal of Physiol. XLIV, p. 237, 1912. 



(6) Barcroft and Poulton, Ibid. XLVI. ; Proc. Physiol. Soc. Feb. 1913. 



(7) Hill, Journal of Physiol. XL. ; Proc. Physiol. Soc. p. iv, 1910. 



(8) Hill, Biochemical Journal, vn, p. 471, 1913 ; Barcroft, Ibid. p. 481. 



(9) Barcroft and Camis, Journal of Physiol. xxxix, p. 118, 1909. 



(10) Barcroft, Ibid. XLII, p. 44, 1911. 



(11) Douglas, Haldane and Haldane, Ibid. XLVI, p. 275, 1912. 



(12) Barcroft and King, Ibid, xxxix, p. 375, 1909. 



