FOXTON-FIRBT : NATURE AND COLOUR OP BLOOD. 



107 



iron-solution, and had been reduced to the purple variety. The purple liquid 

 was now examined with the prism, and the first glance showed that the 

 spectrum was entirely changed. The two lines had vanished, and instead, 

 there was now seen a single line rather less intense than the original ones, 

 and in a position about midway between them. This, then, was clearly the 

 spectrum of purple cruorine, and it could be readily distinguished from that 

 of the scarlet kind. The tube was now shaken with air, so as to bring 

 oxygen in contact with the cruorine. The scarlet colour re-appeared instanta- 

 neously, and in the spectrum the two lines were found to be just as distinct 

 as ever. 



This, however, was not the end of the matter. On allowing the tube to 

 remain at rest for a short time, the purple tint returned, and the spectrum 

 again changed, both being, however, restored to their original condition by 

 agitation. The process, may in this manner, be repeated a number of times, 

 until, in the end, the whole of the iron-solution becomes oxidized, when of 

 course its power ceases. 



Here, then, we have a very simple and beautiful explanation of the 

 mode in which oxidation is carried on in the blood. Cruorine is evidently a 

 substance which has the power of combining -with oxygen, and giving it up 

 again with about equal facility. Blood containing a good deal of purple 

 cruorine (although a large proportion always remains scarlet) passss into the 

 lungs. Here as we before remarked, it is only separated from the air-cells by 

 a tliin membrane kept moist by the blood. The oxygen of the air is dissolved 

 by the water of the membrane, and in this way a constant supply of oxygen 

 is transmitted to the blood. Here it singles out and attracts the purple 

 cruorine, combining with it and converting it into scarlet cruorine. In this 

 state, with all its cruorine in its perfectly oxidized form, the blood sets out 

 from the heart on its race through the body. But these conditions do not 

 last long. The cruorine soon begins to impart some of its newly gained 

 oxygen to the oxidizable matters in its vicinity, which are in this way trans- 

 formed into carbonic acid, water, and, in all probability, other more complex 

 bodies. By the time the blood gets back to the heart, a good deal of its 

 cruorine has been deoxidized, and hence the dark colour of venous blood. 

 It is due entirely to the presence of purple cruorine. In the lungs, the 

 carbonic acid and a portion of the water are thrown off, and a fresh supply 

 of oxygen taken in, so that cruorine plays the part of a conveyor of oxygen 

 from the air to the oxidizable materials, which last, although unable to com- 

 bine directly with oxygen, can yet abstract it easily enough from cruorine. 



