144 



HISTOLOGY. 



globin is readily decomposed into a variety of substances; some of which 

 retain the iron which is a part of the haemoglobin molecule; others lose it. 

 Haematoidin, 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. 168, 2) may be found in old 

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

 Haemosiderin, which contains iron, appears as yellowish or brown granules 

 sometimes extremely fine, ether 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 com- 

 bination of a haemoglobin product with hydrochloric acid is formed, 



called haemin. It crystallizes in 

 rhombic plates or prisms of ma- 

 hogany brown color (Fig. 168, i). 

 Such crystals would show that a 

 suspected stain was a blood stain, 

 but they afford no indication of 

 the species of animal from which 

 it was derived. 



The dimensions of red cor- 

 puscles are quite constant. Those 

 in human blood average 7.5 /JL in 

 diameter and ordinarily vary 

 from 7.2 to 7.8 //. They some- 

 times surpass these limits. In 



biconcave form they are about 1.6 [JL thick. The cups average 7 /< in 

 diameter and are 4 /* in depth. Spherical corpuscles are said to be 5 /^ 

 in diameter. The blood of mammals other than man also contains cups 

 which become discs. The latter are oval in the camel group but round in 

 all others. Their average diameters are less than in man (7.3 ft in the dog, 

 7.48 fjL in the guinea-pig), but the species of animal cannot satisfactorily be 

 determined from the diameter of the corpuscles. It should be noted that 

 the blood of amphibians, reptiles and birds, in the adult contains only 

 nucleated red corpuscles which are oval discs more or less biconvex. 

 They are very large in amphibia (Fig. 169). 



The number of red corpuscles in a cubic millimeter of human blood 

 averages five million for men, and four million five hundred thousand for 

 women. By diluting a small measured quantity of blood and spreading 

 it over a specially ruled slide, the corpuscles may be counted, and the num- 



Leucocyte Side view of 



in motion; at rest. red corpuscles. 



FIG. 169. BLOOD CORPUSCLES PROM A FROG. 



4, 5, and 6, Surface views of red corpuscles; 6, after 



treatment with water. X 600. 



