256 E VOL UTION AND DISEASE. 



deposits constitute the most constant pathological con- 

 dition in gout. 



There is a parasitic affection common in swine 

 (and not infrequently found in man), to which atten- 

 tion has of late years been largely directed, known 

 as trichinosis. The parasite Trichina spiralis when 

 hatched finds its way into the voluntary muscles of 

 man and the pig, there becomes encysted, and in due 

 course is surrounded by calcareous particles. The 

 encysted worms are visible to the naked eye in cut 

 sections of muscle as small dots. In 1866 Virchow 

 detected in a piece of ham some small white concretions 

 which were regarded as trichinae ; but on examination 

 were found to be of crystalline structure, and to furnish 

 the reaction for guanin, a crystalline nitrogenous body 

 resulting from chemical changes in animal tissues, first 

 discovered by Unger in Peruvian guano. 



Guanin seems to be very widely distributed in the 

 animal kingdom ; it occurs in fish, the excrement of 

 spiders, in the pond mussel, the pancreas and liver of 

 the horse, and the skins of frogs and lizards. It responds 

 to easily applied chemical tests. The interest of guanin 

 for us centres itself in the fact that it produces lesions 

 identical in their pathological anatomy with gouty 

 lesions, that is to say, it becomes deposited in cartilage 

 and fibrous tissue, forming deposits exactly resembling 

 the urate of soda deposits in man. Such resemblance is 

 not confined to naked-eye characters, but extends also 

 to the microscopic details as is shown in the drawing 

 (fig. 124), taken from Dr. Mendelson's admirable contri- 

 bution to this interesting subject. When examined in 



