184 THE MICROSCOPIST. 



since they are not laid down in the living body once for 

 all. They are also subject to constant decay, or ultimate 

 decomposition. Histo-Chemistry must, therefore, be always 

 a difficult study, since we can rarely isolate the tissues for 

 examination, nor always tell when a substance is super- 

 fluous aliment, formative or retrogressive material. From 

 a limited number of formative or histogenic materials, we 

 have a host of changed or decomposition products. 



Frey's Histology and Histo-Chemistry, Strieker's Hand- 

 book of Histology, and Beale's Bioplasm, are among the 

 most useful books to the student in this department. 



Frey subdivides the groups of organic principles as fol- 

 lows : 



I. Albuminous or Protein Compounds. Albumen. Fi- 

 brin. Myosin. Casein. Globulin. Peptones. Ferments ? 



II. Hwmoglobulin. 



III. Formative (Histogenic} Derivatives from Albuminous 

 Substances. Keratin. Mucin. Colloid. Glutin-yielding 

 substances. Collagin and Glutin. Chondrigen and Chon- 

 drin. Elastin. 



IV. Fatty Acids and Fats. Glycerin. Formic acid. 

 Acetic acid. Butyric acid. Capronic acid. Palmitic acid. 

 Stearic acid. Oleic acid. Cerebrin. Cholesterin. 



V. Carbohydrates. The Grape-sugar group, Cane-sugar 

 group, and Cellulose group; or Glycogen. Dextrin. 

 Grape-sugar. Muscle-sugar. Sugar of milk. 



VI. Non-Nitrogenous Acids. Lactic. Oxalic. Succinic. 

 Carbolic. Taurylic. 



VII. Nitrogenous Acids. Inosinic. Uric. Hippuric. 

 Glycocholic. Taurocholic. 



VIII. Amides, Amido Acids, and Organic Bases. Urea. 

 Guanin. Xanthin. Allantoin. Kreatin. Leucin. Ty- 

 rosin. Glycin. Cholin (Neurin). Taurin. Cystin. 



IX. Animal Coloring Matters. Hrematin. tLemin. 

 ILiematoidin. Urohsematin. Melalin. Biliary pigments. 



X. Cyanogen Compounds. Sulpho-cyanogen. 



