1882.] Organic Physics. 473 



Hence the energy set free in analysis is only partly needed for 

 new synthesis. Certain changes perhaps take place in the proteid 

 molecules, but the essential work performed is the assimilation of 

 new material, closely similar to the protoplasm of the tissues. 

 For this labor only a tithe of the energy set free by oxidation is 

 requisite, and the remainder is ready for any other employment 

 to which the organism can devote it. If not otherwise employed 

 it becomes temperature energy, but it is also used in two special 

 methods, as nerve and as muscle energy, and organic develop- 

 ment is little more than an increasing specialization of these two 

 modes of energy. 



If now we come to seek the method by which assimilation of 

 protoplasm, and growth of structure, is achieved in the animal 

 body, we shall find it not easy to discover. Albumen is such a 

 highly complex substance, and its chemical composition and 

 changes in constitution are so far beyond the present appliances 

 of chemical science, that we can only proceed by the process of 

 analogy, and seek the possible instead of being able to display 

 the actual. We are apt to speak of protoplasm as if it were one 

 undeviating substance. Yet we might as reasonably speak of the 

 several varieties of starch, of sugar, of woody fiber, of gum, etc., 

 as a single substance. They are only variations of one special 

 form of chemical molecule, and that a comparatively simple one. 

 The molecule of albumen is excessively more complex than that 

 of starch, and is therefore capable of an immensely wider series of 

 variations, without essential change of constitution. And the 

 more complex a molecule becomes the less its internal variations 

 affect its physical constitution. Two simple oxides may differ 

 very widely in physical character. Two unlike sugars present 

 very slight differences. Two diverse albumens may present no 

 appreciable difference. For all we know to the contrary not only 

 the proteid molecules of every special animal tissue may have 

 special constitutions, but also those of every diverse species of 

 animal, and, in a minor degree, of every separate individual. 



When we speak of protoplasm it is far from certain that we are 

 speaking of a homogeneous substance. A mass of protoplasm is 

 made up of chemical molecules which, 





culars. If, indeed, 



> the basic principle of chemical action, we find i 

 i of active affinities. This satisfaction may be c 



