24 LECTURE II. 



under ordinary circumstances. Frommann, Schmitz, Stras- 

 burger and others have succeeded, however, by carefully 

 hardening the tissue and staining the sections, in detecting 

 a more intimate structure. In a young parenchymatous cell, 

 for instance, which is entirely filled with protoplasm, the 

 endoplasm, after hardening and staining, presents a deeply- 

 stained fibrillar network, the meshes being occupied by an 

 unstained more fluid substance ; the ectoplasm presents, not 

 a reticulate but a finely punctated appearance. As the cell 

 increases in size, lacunae are formed in the endoplasm which 

 coalesce to form the vacuole, and the protoplasm (Fig. 3) con- 

 stitutes the primordial utricle and the bridles, as mentioned 

 above. The reticulate structure has, at this stage, almost 

 entirely disappeared, but it may sometimes be observed in the 

 endoplasmic layer of the primordial utricle ; the more delicate 

 bridles appear to be quite homogeneous, whereas the stouter 

 ones present a finely punctated appearance. 



The general conception of the structure of protoplasm 

 which these observations enable us to form is this ; that it 

 consists of a reticulum of fibrillae, enclosing a more fluid sub- 

 stance in its meshes, and that its consistency varies with the 

 size of the meshes, that is, with the proportion of solid and 

 fluid substance of which it is made up. It is probable that all 

 actively living protoplasm possesses this structure. 



With regard to its physical properties, protoplasm, like 

 other organised bodies, is capable of swelling-up, but it has no 

 effect upon polarised light. 



Chemically considered, protoplasm, apart from the meta- 

 plasm and from the substances which are held in solution in 

 the water which saturates it, consists of a mixture of sub- 

 stances which are known as proteids. If a cell which con- 

 tains abundant protoplasm be treated with a dilute solution 

 of potash, it will be found that a considerable quantity of the 

 protoplasm has been dissolved, having a firm framework or 

 reticulum behind, which is dissolved on boiling in strong 

 potash. We may thus distinguish two groups of proteids in 

 the protoplasm, namely, those which are and those which are 

 not soluble in dilute potash. To the second of these two groups 



