400 BLOOD AND LYMPH. 



be carried out as follows: A bit of dried blood is powdered with a 

 few crystals of Nad. Some of the powder is placed upon a glass 

 slide and covered with a cover-slip. By means of a pipette a drop 

 or two of glacial acetic acid is run under the slip, and then by draw- 

 ing the slide repeatedly through a flame the acid is evaporated to 

 dry ness, taking care not to heat the acid so high as to cause it to 

 boil. After the evaporation of the acid water is run under the slip 

 and the specimen is ready for examination with the microscope. 



Hemochromogen(C 3 J:l 3 QN 4 FeO 5 ?) is obtained when hemoglobin 

 is decomposed by acids or alkalies in the absence of free oxygen. By 

 oxidation it is converted to hematin. Hemochromogen is crystal- 

 line, and gives a characteristic absorption spectrum. 



Hematoporphyrin (C 34 H 38 N 4 O 6 ) differs from the preceding deriv- 

 atives of hemoglobin in that it contains no iron. It may be ob- 

 tained from hematin by the action of strong acids, and is of much 

 physiological interest because of its relationship to the bile pigments, 

 which, like it, are iron-free derivatives of the hemoglobin. In old 

 blood-clots or extravasations it has long been known that a colored 

 crystalline product may be formed. This product was designated 

 as hematoidin by Virchow and later was stated, on the one hand, to 

 be identical with the bile pigment, bilirubin, and, on the other hand, 

 to be isomeric with hematoporphyrin. Later observers have 

 prepared from hematoporphyrin by careful reduction a substance 

 designated as mesoporphyrin. It contains one less oxygen atom 

 than the hematoporphyrin, and is claimed to be identical with 

 hematoidin. Another fact of great general interest is that from 

 plant chlorophyl there may be prepared a compound, phylloporphy- 

 rin, very similar to the mesoporphyrin. It would appear from this 

 relationship that the red coloring matter of the blood and the 

 green coloring matter of plants are compounds that have some 

 similarity in chemical structure. 



Histohematins. This name is a general term that has been given 

 to the coloring matter found in the tissues, so far as it has the 

 property of taking up oxygen. The red coloring matter in some 

 muscles is an example of such a compound and has been designated 

 specifically as myohematin. According to most observers, myo- 

 hematin is identical with hemoglobin, that is, the muscle substance 

 contains some hemoglobin, and we may suppose that its presence 

 in the tissue furnishes a further means for the transportation of 

 oxygen to the muscle protoplasm. 



Bile Pigments and Urinary Pigments. Both of these pigments are 

 referred to in the description of the composition of bile and urine. 

 In this connection the fact may be emphasized that each of them is 

 supposed to be derived from hemoglobin, and each constitutes, so 

 to speak, a form of excretion of hemoglobin. 



