I0l8 VERTEBRATED ANIMALS 



fabric is composed of organic matter in two states : the protoplasmic 

 (which he termed germinal matter), possessing the power of selecting 

 pabulum from the blood, and of transforming this either into the 

 material of its own extension or into some product which it 

 elaborates ; whilst the other, which may be termed formed material, 

 may present every gradation of character from a mere inorganic 

 deposit to a highly organised structure, but is in every case altogether 

 incapable of self-increase. A very definite line of demarcation can 

 be generally drawn between these two substances by the careful use 

 of the staining process ; but there are many instances in which there 

 is the same gradation between the one and the other as we have 

 formerly noticed between the ' endosarc ' and the ' ectosarc ' of the 

 Amoeba. Thus it is on the protoplasmic component that the exist- 

 ence of every form of animal organisation essentially depends ; 

 since it serves as the instrument by which the nutrient material 

 furnished by the blood is converted into the several forms of tissue. 

 Like the sarcodic substance of the rhizopods, it seems capable of in- 

 definite extension ; and it may divide and subdivide into independ- 

 ent portions, each of which may act as the instrument of formation 

 of an ' elementary part.' Two principal forms of such elementary 

 parts present themselves in the fabric of the higher animals, 

 viz. cells and fibres (which are modified cells) ; and it will be 

 desirable to give a brief notice of these before proceeding to describe 

 those more complex tissues which are the products of a higher- 

 elaboration. 



The cells of which a few animal tissues are essentially composed 

 consist, in some cases, of the same parts as the typical cell of the 

 plant, viz. a definite * cell-wall,' inclosing ' cell-contents ' and a 

 ' nucleus,' which is the seat of its formative activity. It is of such 

 cells, retaining more or less of their characteristic spheroidal shape, 

 that every mass of fat, whether large or small, is chiefly made up. 

 In a large number of cases the cell shows itself in a somewhat 

 different form, the ' elementary part ' being a corpuscle of proto- 

 plasm of which the exterior has undergone a slight consolidation, 

 like that which constitutes the ' primordial utricle ' of the vegetable 

 cell or the ' ectosarc ' of the Amoeba, but in which there is no proper 

 distinction between * cell-wall ' and 'cell-contents.' This condition, 

 which is characteristically exhibited by the nearly globular colourless 

 corpuscles of the blood, appears to be common to all cells in the in- 

 cipient stage of their formation, and the progress of their develop- 

 ment consists in the gradual differentiation of their parts, the ' cell- 

 wall ' becoming distinctly separated from the ' cell-contents,' and 

 these from the * nucleus,' and the original protoplasm being very 



edition of Todd and Bowman's Physiological Anatomy, 1867. The principal results 

 of the inquiries of German histologists on this point are well stated in a paper by 

 Dr. Duffin on ' Protoplasm, and the Part it plays in the Actions of Living Beings ' in 

 Quart. Journ. Microsc. Sci. n.s. vol. iii. 1863, p. 251. The Author feels it necessary, 

 however, to express his dissent from Professor Beale's views in one important particular, 

 viz. his denial of ' vital ' endowments to the ' formed material ' of any of the tissues ; 

 since it seems to him illogical to designate contractile muscular fibre (for example) 

 as ' dead,' merely because it has not the power of self-reparation. 



