CHEMICAL EXAMINATION OF THE BLOOD. 345 



the so-called oxyhcemoeyanin, which is found in certain arthropods 

 and molluscs, and in which the iron is apparently replaced by 

 copper. Then again we find among invertebrate animals various 

 violet and purplish-red pigments, the so-called floridins, which are 

 likewise to be classed with haemoglobin, and as we have previously 

 seen, a genetic relationship apparently also exists between haemo- 

 globin and the chlorophyl of plants. These various pigments are 

 collectively spoken of as respiratory pigments, as they are intimately 

 concerned in the transportation of the oxygen of the air to the 

 various tissues of the body, and in the removal of the carbon 

 dioxide which results as a product of cellular metabolism. 



Outside of the blood haemoglobin is found also in striped and un- 

 striped muscle-tissues, and under pathological conditions it may 

 appear in the urine as such. Different haemoglobins apparently 

 exist. It is hence impossible to give a definite formula which ex- 

 presses the constitution of all. An idea of their quantitative ele- 

 mentary composition may be had from the accompanying table : 



Carbon. Hydrogen. Nitrogen. Oxygen. Sulphur. Phosphorus. Iron, 



Chicken 52.47 7.19 16.45 22.500 0.857 0.197 0.335 



The size of the haemoglobin molecule is, like that of all albu- 

 minous substances, very large. For that of dog's blood Hiifner 

 obtained the figure 14,129, which would correspond to the formula 

 C636H l0 2frN" 164 FeS 3 O 181 . It thus contains three atoms of sulphur for 

 one atom of iron, while the haemoglobin of the horse and pig has 

 only two atoms of sulphur for one atom of iron. Of interest 

 further is the presence of phosphorus in the haemoglobin of the 

 goose and chicken. Whether this forms an integral component of 

 the haemoglobin molecule, however, is questionable, and it is quite 

 possible that its presence is owing to a contamination of the coloring- 

 matter with nucleinic acid derived from the nuclei of the red 

 corpuscles. 



Structurally, haemoglobin must be regarded as a proteid, viz., as a 

 compound of an albuminous radicle with another complex organic 

 radicle. This other radicle is here an iron-containing pigment, 

 which may be separated from its albuminous pairling, and is termed 

 hcemochromogen (see below), while the albuminous component is 

 known as globin. These two substances are apparently united in 

 the haemoglobin molecule, through an additional radicle, which is as 

 yet unknown. Haemoglobin, like the nucleoproteids, is dextrorota- 

 tory. 



Globin is a histon, and accordingly presents the following charac- 

 teristic reactions: it is precipitated by ammonia from its solutions in 



