CHEMICAL EXAMINATION OF THE BLOOD. 329 



but little is known, and it has not even been definitely ascertained 

 that the pairling of the coloring-matter is really a lecithin. 



Haemoglobin or its oxy-compound occurs widely distributed in 

 the animal world, and is found not only in the vertebrates, but also 

 in many of the invertebrates. But while in the former it is con- 

 tained in definite cellular elements of the blood, it may also occur as 

 such among certain invertebrate animals. Closely related to it is 

 the so-called oxyhcemocyanin, 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 hemo- 

 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 hemoglobin 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. 



Horse 54.87 6.97 17.31 19.730 0.650 . 0.470 



Dog 54.57 7.22 16.38 20.930 0.568 . 0.336 



Pig 54.71 7.38 17.43 19.602 0.479 . 0.399 



Guinea-pig .... 54.12 7.36 16.78 20.680 0.580 . 0.480 



Squirrel 54.09 7.39 16.09 21.440 0.400 . 0.590 



Goose 54.26 7.10 16.21 20.690 0.540 0.770 0.430 



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 

 C 636 H 1023 N 164 FeS 3 O lsl . 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 



