338 THE BLOOD. 



with an alkaline solution of zinc chloride this spectrum gradually 

 passes into a new spectrum with only two bands, of which one is 

 seen about D, and the other between I) and E. 



Closely related to hsematoporphyrin, apparently, is the phyllopor- 

 phyrin which may be obtained from the ehlorophyl of plants. 

 From its formula, C^H^N/)^ and that of haematoporphyrin anhy- 

 dride, C 32 H 34 N 4 O 5 , it is suggested that both are different oxidation- 

 products of one and the same substance, which is still unknown, but 

 undoubtedly represents the mother-substance of the respiratory pig- 

 ment of both animals and plants. The spectrum of both is practi- 

 cally identical. On distillation with zinc dust phylloporphyrin gives 

 the pyrrol reaction, which is also obtained with the coloring-matter 

 of the blood. 



Hsematoidin. This pigment, which was first observed by Yir- 

 chow in old extravasations of blood, in which it may occur in crystal- 

 line form, is now known to be identical with bilirubin. As a separate 

 substance it therefore no longer merits consideration. Its develop- 

 ment from blood-pigment, however, demonstrates the close relation 

 existing between it and the coloring-matter of the bile (which see). 



I have pointed out that in some of the lower animals haemoglobin 

 is also found, and may occur in the blood either as such or bound to 

 certain cellular elements which may be compared to the red cor- 

 puscles of the vertebrates. In other invertebrate animals we find 

 no haemoglobin, but related respiratory pigments, which are partly 

 violet or purplish red in color, and partly blue. The former com- 

 prise the so-called floridins y of which little is known, while the latter 

 group is represented by the oxy-compound of hsemocyanin. 



Haemocyanin is of special interest, as it is apparently closely 

 related to haemoglobin, but contains copper in its molecule in the 

 place of iron. Unlike haemoglobin, however, haemocyanin is itself 

 colorless, while its oxy-compound, oxyhsemocyanin, presents a beau- 

 tiful blue color. On decomposition oxyhaBmocyanin yields an albu- 

 minous substance, which may be compared to globin, and a copper- 

 containing pigment which corresponds to hsematin. On reduction 

 with ammonium sulphide or on exposure to an atmosphere of carbon 

 dioxide it yields the colorless haemocyanin. On spectroscopic exami- 

 nation haemocyanin and oxyhsemocyanin show a shadow at both ends 

 of the spectrum, which is more marked in the latter ; true absorp- 

 tion-bands, however, are not observed. Neither substance has been 

 obtained in crystalline form, and of their elementary composition wo 

 are also in ignorance. 



Other invertebrate animals contain only lipochromic pigments in 

 their hsemolymph, which probably do not possess a respiratory func- 

 tion however, and in the lowest forms of life, of course, special 

 oxygen-carriers are not required. 



