1 88 2. J Or. in their Relations to Life. 973 



ber of these substances has been carefully worked out. In 

 the formation of sugar (C n H.„O n ), starch (C 1 .,H 20 O 10 ), gum 

 (C 12 Ho- n O I3 ), etc., the proportion of oxygen is quite large, and the 

 phenomena of crystallization may occur under certain circum- 



The oils are a still more complex group, being formed by the 

 union of very feeble acids with the common base, glycerine 

 (C,H 8 0,). They are colloidal under all conditions, and decom- 

 pose much more easily than the amyloids. 



The most important organic compounds, however, especially 

 from the biological point of view, are those containing nitrogen. 

 These fall under two general classes, and constitute the so-called 

 organic bases on the one hand, and the albuminoids on the other. 

 The former of these groups have been for the most part extracted 

 from vegetables of which they constitute the " active principles," 

 or characteristic properties, although, as we saw, a large number 

 of them have been artificially manufactured. As illustrations of 

 the nature and composition of these substances may be mentioned, 

 morphine (Q.H^NO,), narcotine (C K H S1 N0 7 ), quinine (C,„H, 4 

 Nj0 2 ), strychnine (C,,H,,N,0.,), etc. It will be seen that the 

 principal particulars in which these fundamentally differ from the 

 organic compounds already considered, consist in the addition of 

 a small percentage of nitrogen and the reduction of the propor- 

 tion of oxygen ; yet the properties which they possess are a 

 hundred-fold more active. 



The composition of the organic bases, however, though some- 

 what complex, is simple compared with that of the albuminous 

 compounds. These contain, in addition to the elements of the 

 former, small, but rather definite proportions of both sulphur and 

 phosphorus. The number of molecules of each of the compo- 

 nents indicates a large, complex molecule as the unit of compo- 

 sition. The expression for albumen as given by Liebig was : 

 QirHsX^A*. Could this be relied upon this substance 

 would contain 679 equivalents of different weights, which, when 

 reduced to the standard of hydrogen, would indicate a molecule 

 for albumen 4870 times as large as the hydrogen unit. The mole- 

 cule of fibrin is supposed to be still larger than that of albumen. 



The substances thus composed, as we should naturally exoect, 

 are very unstable and possess remarkable properties. They con- 

 stitute the substance of the muscles and nerves of the animal sys- 



