438 BLOOD AND LYMPH. 



may be obtained from small quantities of blood stains, etc., no 

 matter how old, and they have been relied upon, therefore, as a 

 sure and easy test for the existence of blood, that is, hemoglobin. 

 The test is one that has been much used in medicolegal cases, and 

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

 a few crystals of NaCl. 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 

 dryness, 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 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 crystalline, and 

 gives a characteristic absorption spectrum. 



Hematoporphyrin (CssHagN^e) 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 pig- 

 ments, 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 hematoi'din 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. It is also 

 of interest to recall that the green coloring matter of the plants, 

 chlorophyl, appears to contain pyrrol groupings, and some of its 

 derivatives show close relationship to derivatives of the hematin. 



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. 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, ahd each constitutes, so 

 to speak, a form of excretion of hemoglobin. 



Origin and Fate of the Red Corpuscles. The mammalian red 

 corpuscle is a cell that has lost its nucleus. It is not probable, there- 

 fore, that any given corpuscle lives for a great while in the circulation. 



