92 GENERAL PHYSIOLOGY. 



relation to health or disease, or, separately, of the muscular, nervous, 

 and plastic forces, or of the force of the arm, the heart, or the thorax, 

 or of the secreting force of a gland, or of the solvent or digestive force 

 of the gastric juice. We shall hereafter see reason to regard most of 

 the so-called forces, thus assumed to operate in the body, as modifica- 

 tions of that common force which, in the inorganic world, is supposed 

 to act in various modes, sometimes by attraction as in cohesion and 

 gravitation the latter being often a cause of visible motion ; some- 

 times as an invisible motion, causing heat ; at other times as light, or 

 electricity, or chemical affinity ; all which phenomena are supposed to 

 be due to correlated manifestations of one and the same universal force 

 pervading all matter. In living animal bodies, we need no longer 

 assume the presence of so many distinct and peculiar forces as were 

 formerly admitted. As we have seen, all the vital actions of animals 

 may be referred to three primary properties, contractility, nervous 

 excitability, and the organizing property. But even for the explanation 

 of these, we do not require to assume the existence of three corre- 

 sponding and purely vital forces, entirely unrelated to the supposed com- 

 mon force of nature ; for the contractility of muscle, the simple excitabil- 

 ity and conductility of the nerve-substance, and the assimilative or meta- 

 bolic affinity of the tissues, though truly named vital properties, as 

 being only exhibited by living bodies, may all depend on, or rather 

 may be merely modifications or special manifestations, within the liv- 

 ing organism, of the common force of nature, acting either mechani- 

 cally, osmotically, electrically, or chemically. Even the higher exci- 

 tability of the nervous cells, manifested in actual sensation and its 

 mental consequences, does not, as already pointed out, escape associa- 

 tion with such corporeal changes as may well be regarded as dependent 

 on vito-physical and vito-chemical modes of action of that common 

 force. But there remains a mystery in this manifestation of feeling 

 and consciousness in connection with matter, even when contemplated 

 in the case of animals, which no physical hypothesis has yet cleared 

 up. Moreover, the vital phenomena dependent on the higher organ- 

 izing or metamorphic property, cannot at present be so explained ; nor 

 is it easy to conceive the possibility of so explaining them, by refer- 

 ence merely to mutations of the universal physical force, which undoubt- 

 edly subserves, and is essential to, their manifestation. 



The formation of a fluid or solid mass of albuminoid protoplasm, 

 may be conceived to be due to a vito-chemical process, and its mainte- 

 nance to vito-chemical changes; but the shaping of this to an organic 

 form, whether a nucleus, a naked nucleated cell or gymnoplast, or a 

 perfect cell with envelope or cystoplast, or the multiplication, modifi- 

 cation, and adhesion of these in definite order, manner, and connec- 

 tion, to form a complex animal or vegetable, implies the presence of 

 some further controlling power. There would seem, indeed, to be 

 some special force in animals and plants, by which the tissues, parts, 

 and organs are evolved in determinate shape, size, and position, and 

 are definitely endowed with their ordinary properties; and by which, 

 moreover, entire organisms are developed in apparently endless varia- 

 tion, according to the distinctions of kingdoms, classes, orders, genera, 



