18 



THE COMPOSITION OF LIVING ORGANISMS. 



less matter enclosing spaces filled with air or water (Figs. 3 

 and 4). 



Among animals analogous cases are common. The muscles 

 of the small intestine, for instance, (Fig. 5), consist of bundles 

 of elongated cells (fibres) each of which is composed of living 

 matter surrounded by a very thin covering (sheath} of lifeless 

 matter. In cartilage or gristle, which covers the ends of many 

 bones (Fig. 6), the oval cells are very widely separated by the 

 deposition between them of large quantities of solid lifeless mat- 

 ter forming what is known as the 

 matrix. In blood (Fig. 7) the flat- 

 tened or irregular cells (corpuscles) 

 are separated by a lifeless fluid 

 (plasma} in which they float. In 

 bone (Fig. 8) the cells have a 

 branching, irregular form, and are 

 separated by solid calcareous mat- 

 ter which is unmistakably lifeless. 

 These examples show that the life- 

 less matters of the body often oc- 

 cur in the form of deposits be- 

 tween living cells by which they 

 have been produced. In all such 

 cases the embryonic tissue consists 

 at first of living cells in direct 

 contact, or separated by only a 

 very small quantity of lifeless mat- 

 ter. In later stages the cells may 

 manufacture additional lifeless 

 substance which appears in the form of solid partition-walls be- 

 tween the cells, or as a matrix, solid or liquid, in which the 

 cells lie. 



Equally important is the formation of lifeless matter within 

 cells, either (a) by the deposition of various substances in the 

 protoplasm. <>r (/ by the direct transformation of the whole mass 

 of protoplasm. Examples of the first kind are mineral crystals, 

 (Fig. 9), grains of starch (Fig. 9), drops of water, and many 

 other substances found withm the cells of plants. Among ani- 

 mals drops of fat (Fig. 10) and calcareous or siliceous deposits 

 are similarly produced. Indeed, there is scarcely any limit to 



FIG. 8. (Modified from Schenk.) Sec- 

 tion of bone from the human femur 

 showing the living branching bone- 

 cells lying in the bony lifeless mat- 

 rix. Diagrammatic. 



