138 ANIMAL. 



certain temperature, intercourse with the air constitutes their vitality, and endows them 



of the atmosphere, supplies of aliment, and with their various cognizable properties, all we 



the access of light, and it is indubitable that can say is that it appears to inhere immedi- 



organized beings exhibit phenomena that ately in the particular state of matter which 



may be designated excitability, irritability, composes them. What this state is in itself 



vital force, &c., which are only other names we cannot tell ; but we are familiar with the 



for these manifestations ; but it is also certain phenomena which ensue from, and which in- 



that external conditions are of themselves ina- deed reveal to us its existence. It is evidently 



dequate to originate manifestations of vitality, as diversified as species, and as the systems or 



and that the phenomena of living organized organs possessed by the individuals severally 



beings, generally designated excitability, irrita- composing these : there is a power the nisus 



bility, incitability, &c., are consequences of a formations, the vis plastica, in the matter sus- 



state of things to explain which they have been ceptible of formation, the organic globule, the 



conceived as causes, under the title of life, germ, which presides over and regulates its 



vital principle, soul, &c. The term excitability acts; and there are powers inherent in the parts 



should be used in physiology, in the very or organisms to which the plastic force gives 



widest sense, to signify a property inherent in rise, in accordance with which they manifest 



organized matter generally, to be determined the special acts that distinguish them. It 



to manifestations of activity under and in con- would be improper, however, to regard this 



formity with external influences (Tiedemann). power or these powers as forces apart from 



We in fact see organized matter of every de- and other than the globules, germs or organisms 



scription the green matter of Priestley, con- themselves ; in the present state of our know- 



fervae, infusory animals, &c., acquiring organic ledge we cannot separate exciting causes from 



forms under the dominion of outward influences, manifestations of activity; all we can venture 



and every species of organized being existing to say is that germs exist, that organisms exist 



within a determinate circle of external agency. with inherent capacities of action in harmony 



It. were a grave mistake to suppose this with the peculiar states of their constituent 

 agency either chemical or mechanical in its na- elements, thus: the germ of the infusory ani- 

 ture ; when of such potency as to act either mal exists with its inherent capacity to en- 

 chemically or mechanically it is destructive gender an infusory animal, the germ of the 

 instead of productive of vital phenomena, polype with its inherent power to produce a 

 These phenomena, therefore, and external polype; in the same way the various tissues, 

 influences are rather in opposition to one vessels, glands, &c. of vegetables and animals 

 another than identical. External influences ex- exist with their special capacities of excitation, 

 cite organized beings to manifest their inherent which are manifested in the particular functions 

 capacities; they do not bestow these capacities ; they severally perform. Excitability is there- 

 all organized beings, indeed, and each parti- fore a multiform property and a consequence, 

 cular tissue of every individual among them, not a single peculiar power inherent in orga- 

 are excited in different modes by the various nized beings, the fundamental cause of their 

 influences from without ; the stimulus is iden- actions and identical with or itself the living 

 tical, the effects are infinitely different. principle. Dependent on the integrity and 



But organized beings, and especially ani- continuance of the functions of nutrition, how 

 mals, are not dependent on external influences can it be the cause of these? Only manifested 

 alone for the manifestation of their peculiar in kind, with the occurrence of specific organs, 

 properties; they have themselves the additional how can it be the cause of their several ma- 

 power of engendering stimuli proper to arouse nifestations ? 



into activity the various organs and systems of We are altogether in the dark with regard 

 which they are composed. The fluids circu- to the mode in which the motions and other 

 lating through every part of their bodies may actions of organized beings are performed, how 

 be regarded in the light of the most generally or by what law the globule that in the infusion 

 distributed stimuli of this description. The of organic matter is to become an infusory 

 nrevous system is another and important source animal moves, as well as of the manner in 

 of excitation, the influence of which is felt in which the contractility of a muscle is excited 

 every part of the organism of all animals above by the stimuli fitted to call this quality into 

 the very lowest. The various instincts, appe- action. The contractility of the infusoria, po- 

 tites, propensities, sentiments, and intellectual lypi, medusae, and other similar tribes appears 

 faculties, also, which all emanate from the to be peculiar. The motions exhibited by the 

 nervous system, are inherent causes of a vast confervae, tremellae, and simplest vegetables 

 variety of manifestations of activity among the are also peculiar to them, they differ from 

 more perfect animals. There are yet other those manifested by the simplest animals in 

 stimuli of a mechanical, or chemical, or pecu- being entirely under the influence of external 

 culiar nature, which excite unusual or ano- influences, and showing nothing like spon- 

 malous manifestations ; m this category may taneity. The tissues of all animals, even the 

 be placed contagions of different kinds, the most complicated, show traces of a vital ten- 

 causes of epidemic diseases, medicines, &c. sion or contractility, different from simple 



With regard to the essence or cause of this elasticity and not depending on muscularity; 



property of the organic globule to commence, the cellular membrane, skin, fibrous tissues 



and pf the perfectly developed organism to generally, excretory ducts, and vessels of all 



manifest the various phenomena whose sum descriptions tend to contract upon the parts 



