ao6 LECTURE XIIJ. 



would necessarily be altered, because the combination of the atoms of different 

 kinds would be loosened. Thus carbon dioxide consists of molecules, each d 

 which is composed of one atom of Carbon and two atoms of Oxygen. In like 

 manner water consists of molecules, each of which consists of two atoms of 

 Hydrogen and one atom of Oxygen. The molecules of most other inorganic 

 compounds are more complicated : the molecule of potassium nitrate, for example, 

 consists of one atom of Potassium, one atom of Nitrogen, and three atoms of 

 Oxygen. The composition of the organic chemical compounds produced by plants, 

 however, are to be conceived as being much more complex. "They all contain Carbon 

 and Hydrogen, and generally Oxygen also, and the most important of all organic 

 combinations — the proteid substances — contain Nitrogen and Sulphur in- addition; 

 and this in sucb a manner that in one molecule dozens, or even hundreds of atoms 

 of the elements named are combined with one another. The body of the plant, 

 then, consists chiefly of such polyatomic chemical combinations. The cellulose of 

 the solid frame-work of the plant, and the protoplasm and nuclear substance 

 consist of molecules, each of which contains very numerous atoms of three, four, 

 or five elements. Even in the province of pure chemistry, however, it is necessary 

 for the explanation of certain phenomena to assume that polyatomic molecules 

 may come together among themselves into closer molecular unions; and that jn 

 this manner new chemical properties arise which do not belong to the individual 

 molecules. 



With chemical processes in the narrower sense of the word are connected other 

 natural phenomena, in which it is no longer merely a matter of chemical changes, 

 but of movements in space of quite another kind. Here belong, on the one hand, 

 those movements of molecules which a dissolved or melted body exhibits on its 

 solidification as a crystal of definite form, as well as those movements by which 

 a crystal becomes again dissolved into its individual molecules, by a soluble medium 

 or by melting ; and, on the other hand, the entrance of water into organised bodies, 

 and the changes in volume effected thereby, as well as numerous other phenomena. 

 We are here particularly concerned with these latter processes, belonging to the 

 domain of molecular physics. For it appears that for the explanation of most 

 processes of life, the assumption of atoms and chemical molecules no longer 

 suffices, but that we are rather obliged to assume combinations of molecules which 

 form very large numbers of small particles, or Micellae (Naegeli), which are never 

 visible with the microscope however, and the arrangement of which gives rise 

 to certain very peculiar properties of organised bodies^. 



^ It is not necessary to go more closely here into the theory of the internal structure of 

 organised bodies founded by Naegeli. Only the following need be noticed. According to Naegeli 

 a series of the most highly characteristic properties of organised bodies — i.p. of starch grains, cell- 

 wallsj and crystalloids— may be explained by the assumption that the molecules in the sense of the 

 chemist are united into larger unions, up to many thousands, and so constitute molecules of a higher 

 order, or, as Naegeli more recently terms them, Micellae (particles). ' Organised substances,' says 

 Nsgeli ('Bot. Mittheilungen' in den Sitzungsberichten der kgl. bayr. Akademie der Wissenschaften, 

 1862, Marz, p. 203), 'consist of crystalline, doubly-refracting molecules (Micellse), which lie near 

 one another loosely, but arranged in a, certain regular manner. In the moist state each of these 

 (Micellse) is surrounded with an envelope of water in consequence of its powerful attraction : in the 

 dry state they are in mutual contact.' In my ' Experimental-Physiologie,' 1865, p, 443, I first 



