IQ4 HISTOLOGY 



bodies, some of which have been considered to be nuclear remains. A 

 few coarse granules of uncertain significance are sometimes conspicuous. 

 The fatty exoplasmic layer which invests the corpuscle and serves as a 

 membrane is not sharply marked out in stained specimens; it appears to 

 blend with the contents of the corpuscle. Although the corpuscles 

 may pass out of the vessels by " diapedesis," they are not actively 

 motile, and their margins never present pseudopodia. The characteristics 

 of haemoglobin may be described as follows: 



Haemoglobin is an exceedingly complex chemical substance which combines readily 

 with oxygen to form oxyhamoglobin. To the latter the bright color of arterial blood is 

 due. Venous blood becomes similarly red on exposure to air. Through the oxyhaemo- 

 globin, oxygen is transferred from the lungs to the tissues. Haemoglobin may be dis- 

 solved from the corpuscles by mixing blood with ether, and upon evaporation it crystal- 

 lizes in rhombic shapes which vary with different animals. Those from the dog are 

 shown in Fig. 185, 4; in man they are also chiefly prismatic. Haemoglobin is readily 



4 



FIG. 1 8s- 1 Haemin crystals and 3, haematoidin crystals from human blood; a, crystals of common salt 

 (X 560); 4, haemoglobin crystals from a dog (X 100). 



decomposed into a variety of substances, some of which retain the iron which is a part 

 of the haemoglobin molecule, others lose it. Hcsmatoidin, considered identical with a 

 pigment (bilirubin) of the bile, is an iron-free substance occurring either as yellow or 

 brown granules, or as rhombic crystals. The crystals (Fig. 185, 3) may be found in old 

 blood extravasations within the body, as in the corpus luteum of the ovary. Hcemo- 

 siderin, which contains iron, appears as yellowish or brown granules sometimes ex- 

 tremely fine, either within or between cells. The iron may be recognized by the ferro- 

 cyanide test which makes these minute granules bright blue. If dry blood from a stain 

 is placed on a slide with a crystal of common salt the size of a pin-head, and both are 

 dissolved in a large drop of glacial acetic acid which is then heated to the boiling point, 

 a product of haemoglobin is formed, called hamin. It crystallizes in rhombic plates or 

 prisms of mahogany brown color (Fig. 185, i). Such crystals would show that a sus- 

 pected stain was a blood stain, but they afford no indication of the species of animal 

 from which it was derived. 



The duration of the life of mature red corpuscles is unknown, but is 

 supposed to be brief. They may be devoured intact by phagocytes, but 

 generally they first break into numerous small granules. These may be 

 ingested by certain leucocytes, or by the peculiar endothelial cells of the 

 liver. Their products are thought to be eliminated in part as bile pig- 

 ment. The destruction of red corpuscles occurs especially in the spleen 

 and haemolymph glands; to a less extent in the lymph glands and red bone 

 marrow. Pigmented cells in some of these structures derive their pig- 



