242 



THE MICROSCOPIST. 



FIG. 197. 



urates into articular cavities, and the parenchyma of the 

 cartilage, bones, and membranes of the joints of gouty 

 persons. It is most common in the cartilage cells (Fig. 

 196). 



The uric acid infiltration acts as a mechanico-chemical 

 agent to the affected parts, producing oedema, suppura- 

 tion, caries, etc. 



3. Pigmentation. 



All true pigments are derived from the coloring matter 

 of the blood. Many of them are elimi- 

 nated by the kidneys and liver, but some 

 are deposited in the tissues, as the choroid 

 coat of the eye and the rete Malpighii of 

 the skin. Some pathological cases may 

 be ascribed to extravasation or some local 

 stasis in the circulation ; others may be 

 caused by wandering leucocytes (page 

 188). The brown atrophy of the muscu- 

 lar tissue of the heart, which is often as- 

 sociated with marasmus, is caused by the 

 deposit of yellow granular pigment in the 

 muscular fibre (Fig. 197). 



The dark pigment of the lungs owes 

 its origin chiefly to the respiration of 

 carbon in the shape of particles of soot, 

 coal-dust, etc., floating in the atmosphere. These parti- 

 cles are first taken up by the mucous corpuscles (leuco- 

 cytes) of the trachea and bronchi, and many of them are 

 expectorated. Some, however, make their way to the 

 air-vesicles, and penetrate the alveolar walls and inter- 

 lobular tissue (Fig. 198). 



In the case of coal-miners the lungs often become uni- 

 formly black. Workers in iron-dust are liable to have 

 the lungs stained red from oxide of iron, and stonecutters, 

 etc., to inhale and deposit silicic acid or fine sand. Such 



Brown atrophy of 

 heart-muscle. Frag- 

 ment of a membrane 

 of muscular fibres, 

 with pigment-gran- 

 ules in the interior 

 of the primitive bun- 

 dles. 1-300. After 



RlNDFLEISCH. 



