Chap, ii.] BLOOD. 13 



The elements of the blood described by Dr. William 

 Norris, of Birmingham, as the invisible, pale, or third 

 corpuscle, are simply red blood corpuscles that have 

 become discoloured by the mode of preparation 

 (Alice Hart). 



1 2. The haemoglobin of the red blood corpuscles 

 forms crystals (Fig. 10), which differ in shape in the 

 various mammals. 

 They are always 

 of microscopic size, 

 and of a bright red /j\ 



colour. 



In man and 

 most mammals 

 they are of the 

 shape of prismatic \^- -j 



needles, or rhombic jj^\ ^^^o 



plates ; in the p . g 10 _ H8emoglobin crystals . 



Squirrel they are A Of gu i nea . p jg ; B> O f squirrel ; c, D, human. 



hexagonal plates, 



and in the guinea-pig they are tetrahedral or octa- 

 hedral. The blood pigment itself is an amorphous 

 dark-brown or black powder the hcematin ; but it 

 can be obtained in a crystalline form as hydro- 

 . chlorate of hematin(Fig. 11). These crystals 

 also are of microscopic size, of a nut-brown 

 '4 colour, of the shape of narrow rhombic 

 ' plates, and are called hcemin crystals, or 

 Teichmann's crystals. In extravasated 

 human blood crystals of a bright yellow 

 or orange colour are occasionally met with ; they are 

 called by Virchow, their discoverer, hcematoidin. 

 They are supposed to be identical with bilirubin, 

 obtainable from, human J&ile. 



13, The white or colourless blood cor- 

 puscles are' in human blood of about -^ ^Vo to ^wo- 

 of an inch in diameter, and are spherical in the 

 \ 



