CHEMICAL PROCESSES IN CELLS. 151 



external force ; but in such a process as the manufacture of fat out of 

 carbo-hydrates, or the synthesis of albuminoids out of carbo-hydrates 

 and inorganic nitrogenous compounds, or the formation of starch, 

 cellulose, etc., out of glucose, the potential energy developed is not 

 derived from an external force, as the light in chlorophyll plants, but 

 from a force inherent in the cell itself. This force is manifested in the 

 oxidation processes occurring in colorless protoplasm, and which are 

 evidenced by the excretion of C0 2 and H a O as combustion products. 

 Thus, in the synthesis of higher carbo-hydrates from glucose a combus- 

 tion results, in which H a O is formed, and in it the two atoms H and 

 are more closely united with one another; in this process potential energy 

 is transformed into actual force. In order to comprehend the formation 

 of fat or albuminoids out of oxygen compounds without a simultaneous 

 liberation of oxygen there must also always be an additional combustion 

 of ■ loosely-combined carbon into CO,; from this it follows that pure 

 oxidation processes occur in such cells, such as the formation of 

 vegetable acids out of carbo-hydrates, volatile acids from fixed fatty 

 acids, — processes which yield a certain amount of actual energy in the 

 form oT heat, of which a part is again rendered latent in the formation of 

 chemical potential energy. As a whole, in cells free from chlorophyll the 

 processes accompanied by the liberation of actual .forces preponderate 

 over those in which actual energy is consumed. In every such cell, 

 therefore, there is an actual development of heat. A small part of this 

 actual energy, before being converted into heat, may be transformed into 

 the mechanical movements already described. Every independent organ- 

 ism which is free from chlorophyll manifests changes which result in the 

 same transformation of force as described above ; such examples are seen 

 in the case of the organized ferments. 



The animal cells, on the other hand, directly appropriate highly 

 complex substances, such as albumen, fats, and carbo-lrydrates, in which 

 a high degree of potential energy is contained. In the act of forming by 

 oxidation simpler compounds, such as C0 2 ,H 2 0, and NH S , their potential 

 energy is transformed into actual force, partly manifested by heat- 

 production, and by protoplasmic contractile movements. In animal cells, 

 therefore, the main characteristic is the conversion of the potential 

 energy of organic compounds into the actual forces of heat and 

 mechanical movements ; the process being much the same as has already 

 been referred to as occurring in the vegetable cells free from chlorophyll, 

 differing mainly in intensit.y. A reverse process maj' be also present by 

 which actual force may be consumed and potential energy stored up, as 

 in the formation of complex albuminoids, such as haemoglobin, or in the 

 re-formation of albumen out of peptones. 



