THE BLOOD-CORPUSCLES. 181 



from the properties of haematin, as described in the first volume, 

 we should scarcely expect such an action ; for we have there seen 

 how indifferent and inaccessible haematin is to most chemical 

 reagents; but, on the other hand, it is also manifest that this 

 pigment can hardly exist in the blood-cells in the same state in 

 which it is exhibited isolated by chemists. There is still a perfect 

 absence of definite chemical facts to prove the almost indubitable 

 action of oxygen on the contents of the blood-corpuscles ; there 

 are merely a few experiments made by Bruch* in support of this 

 view, which has become more than probable from physiological 

 grounds. The pigment itself appears to undergo changes of 

 colour by oxygen and carbonic acid ; for if strongly watered blood, 

 in whose plasma it may be presumed that the contents of the 

 blood-corpuscles are diffused, be shaken with carbonic acid gas, its 

 dark colour becomes still darker in refracted (or transmitted) light ; 

 that is to say, blood which is merely watered appears^ when viewed 

 by transmitted light, of a less deep dark red colour than blood 

 which has been similarly watered and has been impregnated with 

 carbonic acid ; we observe the opposite result on treating blood, 

 which has been watered in this manner, with oxygen gas. This may 

 serve to explain why the blood of the portal vein, which is richer 

 in water than that of the other veins, is also of a darker colour. 



Taking into consideration all these circumstances regarding 

 the mechanical relations of the blood-corpuscles, it follows that a 

 definite tint may be given to the whole blood by the action of 

 very different influences upon the blood-cells, and that in special 

 cases it is often very difficult to decide on which of these often 

 opposite causes the colour of the blood in any particular case may 

 depend. 



Moreover, there are other physical relations, not directly acting 

 on the blood-corpuscles, which may modify the colour of the whole 

 blood. Thus we find the blood of a lighter tint when, in addition 

 to the red cells, it contains a very large number of colourless 

 corpuscles, or of other particles which strongly reflect light ; thus 

 Scherer showed that the addition of milk or- powdered gypsum 

 made the blood of a lighter red tint ; and this is also the reason 

 that we sometimes find the blood, in cases of pyaemia and anaemia, 

 which abounds in colourless blood-cells, as well as the blood of 

 confirmed drunkards, in which there are innumerable fat-globules, 

 of a comparatively light tint. 



We need hardly mention that external influences, such, for 

 * Zeitschr. f. rat. Med. Bd. 1, S. 440-450, and Bd. 3, S. 308-318. 



