356 THE BLOOD. 



I have pointed our 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, of which little is known, while the latter 

 group is represented by the oxy-compound of haemocyanin. 



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, oxyhaemocyanin, presents a beau- 

 tiful blue color. According to Frederique, oxy haemocyanin yields 

 an albuminous substance on decomposition with hydrochloric acid as 

 also with nitric acid, which may be compared to globin, and a cop- 

 per-containing pigment which corresponds to haematin. Henzel 

 however, was unable to confirm this observation. He obtained an 

 albuminous body of the character of an acid albumin, but no histon. 

 The copper of the haemocyanin is not present in firm organic combi- 

 nation, but in a loosely combined form, analogous to a copper albu- 

 minate. 



Henze has recently succeeded in crystallizing the haemocyanin, and 

 on elementary analysis obtained the following values : C 53.66 ; 

 H 7.33 ; N = 16.09 ; S = 0.86 ; Cu = 0.38, and O = 21.67. 



On reduction with ammonium sulphide or on exposure to an at- 

 mosphere of an indifferent gas like H, CO 2 , N, etc., the oxyhaemo- 

 cyanin yields the colorless haemocyanin. On spectroscopic examina- 

 tion haemocyanin and oxyhaamocyanin show a shadow at both ends 

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

 bands, however, are not observed. 



Other invertebrate animals contain only lipochromic pigments in 

 their haemolymph, 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. 



