THE CHEMICAL UNITY OF LIVING BEINGS. I77 



importance. We may no longer in these days speak 

 without reservation of the vital vortex of Cuvier, and 

 of the incessant twofold movement of assimilation 

 and dissimilation which is ever destroying living 

 matter and building it up again. In reality, the 

 living protoplasm varies very little; it only under- 

 goes oscillations of very slight extent; it is the 

 materials, the reserve stuff on which it operates, which 

 are subject to continual transformations. 



Chemical Composition of Protoplasm. — One of the 

 the three characters attributed by Ch. Robin to living 

 matter was its chemical composition, of which little 

 was known in his time. He insisted on the constant 

 presence in the living elements of three orders of 

 immediate principles — proteid substances, carbo- 

 hydrates, and fatty bodies. In reality the proteid 

 substances, or albuminoids, alone are characteristic. 

 The two other groups, carbohydrates and fatty bodies, 

 are rather the signs and the products of the vital 

 activity, than constituents of the matter on which it is 

 exercised. 



It is therefore on the knowledge of the proteid 

 substances that all the sagacity of biological chemists 

 has been exercised. Their efforts for thirty years, 

 and particularly in the last few years, have not been 

 barren ; they enable us to give a first rough sketch of 

 the constitution of these substances. 



§ I. The Characteristic Substances of the 

 Protoplasm. The Nucleo-Proteids. 



The Different Categories of Albuminoid Substances. 

 — Albuminoid or proteid substances are extremely 

 complex compounds, much more so than any of those 



