176 BLOOD. 



1 volume of blood, when mixed with half its volume of ex- 

 tremely diluted hydrochloric acid (1 part of hydrochloric acid to 

 532 of water), became very dark ; the blood-corpuscles were not 

 much affected ; they were all a little thicker than usual, and those 

 lying on their edge were baton-shaped. 



On mixing 1 volume of blood with 0*001 of a volume of caustic 

 ammonia, there was scarcely any change of colour, and the blood- 

 corpuscles were not visibly altered ; after 24 hours they sank to 

 the extent of l-100th of the volume ; the serum was then red, and 

 the corpuscles a little distended. 



The caustic alkalies, and several organic acids, as for instance, 

 acetic acid, convert the blood into a blackish brown, thick, tolerably 

 consistent jelly ; and at the same time distend the corpuscles, and 

 distort or destroy them. 



We learn, from the observations of Harless, that the primary 

 action of oxygen and carbonic acid on the coloured cells, is also of 

 a mechanical nature ; but this author has shown, by his variously 

 modified experiments, that these gases likewise exert a chemical 

 influence on every molecule of the blood; thus he found, for 

 instance, that when we allow oxygen and carbonic acid to act 

 alternately on the red cells, they become gradually destroyed, the 

 destruction being usually completed after the ninth or tenth 

 exposure to the action of the gases an experiment which is 

 obviously of the highest importance in connexion with the 

 coloured cells in the circulating blood. We should therefore, at 

 all events, be going too far if, on the above-mentioned grounds, 

 we should ascribe the influence of oxygen or of the gases 

 generally on the colour of the blood, solely on the changes in the 

 form of the blood-corpuscle which they induce. The primary 

 action of the oxygen may always be a physical one, like that of the 

 salts ; but these also act mechanically only at first ; they almost 

 all, as we have already seen, communicate a light red colour to the 

 blood in the first moments of their action ; after a longer or shorter 

 period (varying in the case of different salts), they give a more 

 or less dark red tint to the blood. 



It is in the greater or less rapidity of the mechanical action of the 

 salts, that the reason must be sought why a merely chemical action 

 has been ascribed to many of them, when they were only regarded 

 as capable of darkening the colour of the blood ; as for instance, 

 to the alkaline carbonates, (Mulder and Nasse), the salts of am- 

 monia (Dumas), and the potash-salts, especially nitre (Hiinefeld). 



Nasse has shown from several carefully conducted series of 



