Molecidar Structure in Protoplasm 47 



tertistics peculiar to itself which detract somewhat from its sim- 

 plicity, for, while each water molecule consists of one oxygen and 

 two hydrogen atoms, the atomic nuclei and constituent electrons are 

 so arranged that two residual negative electrical fields and two 

 positive fields occur at tetrahedral points in the molecule (15) . These 

 are effective in making the water molecule a permanent dipole (16) . 

 The more prominent features are indicated in the diagrams of Figure 

 1 and are mentioned because these characteristics are constantly 

 involved in the structure and behavior of protoplasm as well as in 

 the aggregation of the water molecules themselves (17) . The radius 

 of the spherical structure shown in Figure l.A, with two great circles 

 at right angles to each other, is about 1.38 A. At B the effect of the 

 intermolecular plus-minus attractions is shown as in ice where four 

 surrounding water molecules are coordinated tetrahedrally with a 

 central molecule (15. 18). Such groups vary in amount with the 

 temperature; and in themselves vary in number from one and two 

 at the boiling point to a group of several or many near freezing (17) . 



When a portion of the water molecule occurs as a hydroxyl 

 group, — OH, on an organic molecule, one of the plus residual 

 points is missing due to the formation of the primary valence bond; 

 this leaves only three points for coordination with water molecules in 

 the surrounding solution. It is due to the nature of the oxygen atom 

 (19) that these negative residuals occur. Only one other atom, which 

 is of interest to us, is similar in this respect; this is nitrogen (19), 

 which has, however, only one negative residual charge. Thus, what 

 is said of oxygen and OH groups will apply to a considerable extent 

 also to NH and NH. groups. Residuals of this nature are completely 

 lacking in the carbon atom and in CH- groups. 



There seems to be scarcely any need of mentioning here that the 

 four atoms, C, H, O, and N, are the principal components of proto- 

 plasmic molecules and that they make up nearly 99 per cent of 

 active protoplasm. One feature of these atoms which is less com- 

 monly known, although characteristic of the three larger atoms, 

 C, O, and N, was shown in Figure 1. This is the angle at which bond 

 formation occurs. This angle made by adjacent primary valence 

 bonds is practically 109° and is spoken of as a tetrahedral angle 

 (19) . Its occurrence will be noted in figures of the models presented 

 here wherever single primary bonds exist. The angle is relatively 

 rigid and therefore determines the shapes of molecules to a great 

 extent, as may be seen later in the models mentioned where the four 

 bonds of carbon reach out to form a tetrahedral structure; simi- 



