2 DISTRIBUTION OF HEMOGLOBIN AND ALLIED SUBSTANCES 



body is a normal functionating constituent, while in others it is an inci- 

 dental inactive body, being introduced as food, etc. According to March- 

 lewski (Die Cheraie d. Chlorophyll, 1895, 63), chlorophyl isolated from 

 whatever plants is identical, but Montverde (Acta horti Petropolit., 1893, 

 xni, 176) and Etard (Compt. rend. soc. biolog., 1895, cxx, 275) hold that 

 there are various kinds. It is probable that the bodies studied by Mont- 

 verde and Etard were impure. Whichever may be true, there is no doubt 

 that isolated chlorophyl pigment is physiologically inert (page 22) and that 

 the chloroplastids (chlorophyl-protein combinations) differ chemically, 

 physically, and biologically, and that the functionating chlorophyl granule 

 of animal life is not identical with that of plant life. There is evidence 

 of intermediate bodies between chlorophyl and histohematin, as MacMunn 

 has found in Helix pomatia. 



STATEMENT OF THE DISTRIBUTION. 



Hemoglobin is entirely absent from Protozoa, Porifera, and Coelen- 

 terata; it is rare in Echinodermata; it is quite common in certain classes 

 of Annelida; and it is comparatively rare in Arthropoda. (See page 63, 

 Chapter II.) It is distributed among the invertebrates in a remarkably 

 sporadic and inexplicable way, appearing in only certain classes of a series, 

 or in certain members of a class, etc., sometimes exclusively as a constitu- 

 ent of blood corpuscles or blood plasma, or in nervous matter, or in parts 

 of the musculature, etc. It may be present in members of a certain class, 

 as for instance the Choetopoda, but in certain of them it is found as a con- 

 stituent of special blood corpuscles, and in others in solution in the blood 

 plasma. It may be present in certain members and absent in others, and 

 in the latter it may be represented by closely allied bodies, chemically and 

 physiologically, such as the chlorocruorins, histohematins, etc. 



The close chemical relationship of chlorocruorin to hemoglobin is 

 shown in its yielding hematin as a decomposition product, while the histo- 

 hematins are in the nature of modified forms or derivatives of hemoglobin. 

 Chlorocruorin probably exists in several forms or modifications and seems to 

 have a very restricted distribution, limited to the invertebrates, while histo- 

 hematins and myohematins are very numerous among both invertebrates 

 and vertebrates. Closely related to hemoglobin, chiefly physiologically, 

 is hemocyanin, which probably exists in several modified forms. Hemo- 

 cyanin is albuminous and contains copper in the molecule in place of the 

 iron of the hemoglobin molecule; it is distributed solely among the inver- 

 tebrates, but more widely and quite as erratically as hemoglobin. A large 

 number of lipochromes, some closely allied to chlorophyl and hemoglobin, 

 have been found in both invertebrates and vertebrates. 



In all vertebrates, except the Leptocephalus and probably the Amphi- 

 oxus, hemoglobin is present in the red blood corpuscles, but is never 

 normally in solution in the blood plasma. In addition to hemoglobin, we 

 find modifications, compounds, and derivatives as normal constituents of 

 various body fluids and solids. 



