POXTON-FIRBY ; NATURE AND COLOUR OF BLOOD. 



105 



Two well-marked black bands now made their appearance in the green 

 portion of the spectrum, and these had exactly the same position, whatever 

 kind of blood was employed. No other known substance gave similar lines 

 in the spectrum, and the experiment therefore became at once a valuable 

 means of detecting the presence of blood. Here the matter rested, until 

 Professor Stokes, struck with the phenomenon, set to work to investigate 

 it further. It was evident from the very first that the peculiarity must be 

 caused by the colouring matter of the blood. For many years before this a 

 red substance called hcematin had been known, which could be prepared by 

 a chemical process from the blood, and it was therefore iiniversally supposed 

 that the colour of the blood was due to this hsematin. Hence it was clear that 

 a solution of h0em.atin ought to give the same spectrum as the blood from which 

 it was obtained. But on trying the experiment, Professor Stokes soon found 

 that this was not the case. Certain opaque lines, were, indeed, seen in the 

 hsematin-spectrum, but they were utterly different, both in number, intensity, 

 and position from the lines in the blood-spectrum. 



Here, then, was an important discovery, and one which upset at once a 

 universally received physiological tenet. Hcematin is not present in the blood 

 but is simply a substance formed from it by the elaborate and difficult chem- 

 ical operations by which it is prepared. 



Having established this point, it is obvious that the next step to be 

 taken was to endeavour to learn something of the true blood-colour, the un- 

 known something which caused the two black lines in the normal blood 

 spectrum. Not being a professed chemist. Professor Stokes did not attempt 

 to isolate the colouiing matter, but left that task to future investigators. As 

 however, its existence could not be doubted, he gave it the name of Cruorine^ 

 to distinguish it from the haematin already known. 



And now followed a series of experiments upon the nature of cruorine, 

 which revealed some most curious and important facts. In order to make 

 \ them intelligible to the non-physiological reader, it will be necessary to point 

 out in a few words the leading characteristics of the blood in its circulation 

 through the system. As the blood flows on its ceaseless course, it is carried, 

 as every one is aware, thi'ough the lungs. In the minute capillary blood- 

 vessels through which it here passes it is separated by only a thin wall of 

 moist membrane from tiny air-cells which communicate with the external air 

 .' through the bronchial tubes, and in and out of which air is continually being 

 pumped by the act of respiration. The blood which enters the lungs has a 

 dark purple colour, and is known as venous blood j but when it emerges, and 



No. 56, December 1. h 



