28 THE HUMAN BODY 



mediate agent in the manifestation of the vital activities of the 

 cell. So far as the manifestation of the power of movement is con- 

 cerned the evidence seems in favor of the hyaloplasm; the outer- 

 most parts of a white blood-corpuscle, for example, exhibit active 

 contractile power, yet they contain no spongioplastic filaments; 

 and many unicellular living things are known in which no reticular 

 structure can be discovered and which nevertheless nourish them- 

 selves and are reproductive, irritable, contractile, conductive, co- 

 ordinative and automatic. It is therefore possible that the fila- 

 ments when present are to be regarded as secondary in importance 

 to the hyaloplasm, partly serving as a mechanical support; but in 

 addition they may play an important part in the internal econ- 

 omy of the cell. The study of the physiology of individual cells 

 presents very great difficulties and is yet in its beginnings, so that 

 we can do little more than speak of the properties of the cell as a 

 whole, though from the frequent radial arrangement of the cell- 

 protoplasm in its neighborhood and from the part it plays in the 

 initiation of cell division, the attraction-particle appears to have 

 a very important role. 



Of the actual chemical composition of living matter we know 

 only that its molecule is one of great complexity: all methods of 

 chemical analysis break it up and alter it fundamentally, so that 

 what is really analyzed is not living matter but a mixture of the 

 products of its decomposition, among which protein substances 

 are always prominent. 



Cell-protoplasm no doubt varies a little in different cells, so that 

 the name is to be regarded as a general term designating a number 

 of closely-allied substances agreeing with one another chemically 

 in main points, as the proteins do, but differing in minor details, in 

 consequence of which one cell differs from another in faculty. On 

 proximate analysis every mass of protoplasm is found to contain 

 much water and a certain amount of mineral salts ; the water being 

 in part constituent or entering into the structure of the particles of 

 protoplasm, and in part probably deposited in layers between them. 

 Of organic constituents protoplasm always yields one or more 

 proteins, some fats, and some carbohydrates. So that the original 

 protoplasm is probably to be regarded .as containing chemical 

 "residues" of proteins, fats, and carbohydrates, combined with 

 salts and water. 



