ON GENERATION. 341 



pear from our observations what is truly and properly to be 

 called " an efficient." 



Aristotle ' defines an efficient cause to be that " whence is 

 derived the first principle of change or quiescence ; as a coun- 

 sel, a father; and simply as doing that which is done; the 

 transmute of the thing transmuted." In the generation of 

 animals accordingly many and various kinds of cause inducing 

 motion are brought forward; sometimes an accident or quality 

 is assigned; and so animal heat and the formative faculty are 

 called efficient causes. Sometimes it is an external substance, 

 previously existing, in which inheres the plastic force or forma- 

 tive faculty that is designated in the same way ; as the cock or 

 his seminal fluid, by the influence of which the chick is pro- 

 created from the egg. Occasionally it is some internal sub- 

 stance, self-existent, such as spirit, or innate heat. And again, 

 it is some other substance, such as form, or nature, or soul, 

 or some portion of the vegetative soul, that is regarded as the 

 efficient, such a principle as we have already declared to inhere 

 in the egg. 



Besides, since one thing whence motion proceeds is nearer 

 and another more remote, it sometimes happens that the media 

 between the prime efficient and the thing last effected, and in- 

 struments are regarded as efficient causes ; subordinate conclu- 

 sions, likewise, or the principles of subsequents, are reckoned 

 among the number of efficient causes ; in this way some parts 

 are themselves spoken of as genital parts, such as the heart, 

 whence Aristotle affirms that all the rest of the body is pro- 

 duced ; a statement which we have found borne out by our 

 history. The heart, I repeat, or at all events its rudimentary 

 parts, namely, the vesicle and pulsating point, construct the rest 

 of the body as their future dwelling-place ; when erected it enters 

 and conceals itself within its habitation, which it vivifies and go- 

 verns, and applying the ribs and sternum as a defence, it walls 

 itself about. And there it abides, the household divinity, first 

 seat of the soul, prime receptacle of the innate heat, perennial 

 centre of animal action ; source and origin of all the faculties ; 

 only solace in adversity ! 



Moreover, since the " efficient " is so styled with reference 



1 Metaph. lib. v, cap. 2 ; et Phys._lib. ii, tit. 28. 



