126 Rev. P. Keith on the Conditions of Life. 



upon substances that are still in an organized state, yet they 

 cannot convert them into nourishment till they have destroyed 

 their organization in the stomach. Is it certain that all animals 

 require a food that has once been organized ? What is the 

 food of Cancer salinns ? 



A better criterion for distinguishing the animal from the 

 plant will be found in the attribute of sensation. For though 

 there may be some phaenomena that give countenance to the 

 idea of vegetable sensibility, yet they are not such as the phy- 

 siologist can confidently rely upon; and as the attribute of 

 sensation distinguishes the animal from the plant, so their as- 

 sumption and assimilation of aliment, and their origin and 

 mode of growth, will distinguish them both from the mineral. 

 If this last criterion had been kept in view, the noted definition 

 of Linnasus would have been less incorrect: ^^Lapides crescunl; 

 vegetahilia crescunt et vivimt ; animalia crescunt, vivunt, et sen- 

 tiunt*" — Stones grow; plants grow, and live; animals grow, 

 live, and feel. But the truth is that stones do not grow in the 

 sense in which plants and animals grow; not by the intro- 

 susception and distribution of aliment throughout their whole 

 substance, but merely by the apposition of new particles added 

 to the external surface. In this respect the definition is faulty. 

 In other respects it is perhaps well enough ; and in brevity 

 and decision of tone it will not be easily surpassed. 



Upon the principle which we adopted in our definition of 

 life, namely, that of a copious enumeration of particulars, I 

 submit the definitions that follow, with a view to mark out the 

 boundaries of the three kingdoms of nature : — A mineral is a 

 mass of lifeless matter, inorganic, inert, insentient; not aug- 

 mentable by nutrition, but attaining its bulk merely by the 

 external and mechanical or chemical apposition of new parts 

 or particles. — A vegetable is a living and organized body, inert, 

 insentient; springing from and producing a germ that is aug- 

 mentable by nutrition ; and fixed, by a root, to the soil, from 

 which it absorbs its principal nourishment already in a fluid 

 state. — An animal is a living and organized being, self-moving, 

 sentient; springing from and producing a germ that is aug- 

 mentable by nutrition, and ranging in quest of aliment, which 

 it takes up chiefly in a solid state, and subjects to the action 

 of digestive organs. 



There are assignable limits, then, which separate the thi'ee 

 kingdoms of nature ; between the mineral and vegetable, orga- 

 nization ; between the vegetable and animal, sensation. In 

 an unorganized body there is no community of interests among 

 the different parts, and no part that is necessary to the well- 



* Philosnphia Bolanica. 2. 



being 



