CHAP. IL] THE BLOOD. 105 



He demonstrated, further, that when blood is shaken up with carbonic 

 oxide, not only does it become florid, but an exchange of gases takes 

 place, the loosely combined oxygen of the blood being expelled from 

 it, and its place taken by an equal volume of carbonic oxide. 



After the discovery by Hoppe-Seyler and Stokes of the remarkable 

 spectroscopic properties of the blood-colouring matter, attention was 

 paid to blood which had been treated with CO, and it was found 

 that whilst the spectrum of such blood is almost identical with that 

 of oxy-haemoglobin, it possesses the property of resisting the action 

 of reducing agents. 



Subsequently, Hoppe-Seyler found that after passing a stream of 

 CO through a solution of oxy-haemoglobin, and then adding alcohol, 

 on exposing the mixture to cold, crystals separated which were 

 identical in form with those of oxy-haemoglobin, but the solution of 

 which was unacted upon by the agents which reduce oxy-haemoglobin. 



From all these observations it resulted that carbon mon-oxide 

 possesses the power of displacing the respiratory oxygen which 

 exists in a state of loose chemical combination with haemoglobin, and 

 of forming a compound possessed of nearly the same physical 

 properties but differing from it in being much more stable ; further 

 from the fact that, in the formation of this compound, one volume of 

 oxygen is exactly replaced by one volume of carbon mon-oxide, it 

 follows that a molecule of the latter takes the place of a molecule of 

 the former. 



Although the spectrum of CO-haemoglobin very much resembles 

 that of oxy-haemoglobin, there are minute differences which are 

 shewn by comparing the spectra of the two bodies existing in a 

 solution of the same strength, and examined under precisely similar 

 circumstances. It will be seen (Fig. 22, spect. 6 compared with 

 spect. 2), that in the CO-haemoglobin both the bands a. and /3 

 are moved very slightly nearer the violet end of the spectrum. 

 Amongst other points of difference between the CO- and 0- com- 

 pound, we have to mention that the crystals and solutions of the 

 former have a tinge of blue which is wanting in the latter, and 

 that the crystals of CO-haemoglobin are slightly less soluble than 

 those of 2 -Hb. 



So far as the Author is aware, Jaderholm 1 and Sorby are the only observers 

 who have stated the position of the bands of oxy-haemoglobin and of CO-hae- 

 moglobin in wave-lengths. According to Jaderholm the centre of oxy-haemo- 

 globin a corresponds to W. L. 5730, of ft to 5370. On the other hand the 

 centre of CO-haemoglobin -a corresponds to W. L. 5690 and of ft to 5340. 

 These determinations do not agree with those of Preyer, nor with indepen- 

 dent observations of the Author. In the first place the centre of these 

 bands is not constant for solutions of different strengths, for it will be found 

 that the band j3 extends more towards the blue than the green as the 

 concentration of the solution increases. According to Sorby the centre 



1 Jaderholm; see abstract by Hammarsten in Maly's Jahresbericht, vol. iv. p. 106. 



