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caloric is capable of an analysis, by combination with an ovum, 

 into a thousand constituent properties, each of which made its 

 specific constitution. But we cannot indulge this supposition to 

 any extent, because we find that instead of being broken down 

 into all those constituents by which, according to our principle 

 of causation, it would cease to be heat; instead of this, we find 

 that it pervades all parts in its own form, and has no other per- 

 ceptible agency than that of increasing the temperature of the 

 ovum, thus operating by a general relation, and preserving its 

 entire nature, and not by a relation subsisting between its analysed 

 properties and those of the ovum. 



18. But these proofs being, as thus stated, not unexception- 

 able, even with respect to our^laws of causation, it is right before 

 we admit an inference from them to scrutinize the matter a little 

 deeper. It is said in the last paragraph that heat cannot preserve 

 its own identity, and produce a great variety of effects by a true 

 process of causation; that is, by supplying the respective causes 

 which are necessary to different effects. But this observation holds 

 good only of the operation of heat upon substances which preserve 

 their identity, or which maintain the unity of their constitution 

 under its influence ; in such, their nature is still preserved, their 

 temperature only is raised, and is not applicable to compound sub- 

 stances, or those disposed to separate their constituents, among 

 which the ovum may be reckoned as one ; in these latter, heat, with- 

 out ceasing to be recognizable, may have several relations with con- 

 stituents, and produce several effects. Thus, as familiar examples, 

 heat may deliquate wax, which will still remain the same in consti- 

 tution, though rendered fluid by its combination with heat; or it 

 may fuse different metals, or ignite a combustible substance, or 

 deprive a fluid apparently homogeneous of its spirit, or its oil, &c. ; 

 that is, it will afford to each of these substances (which are dissimi- 

 lar) an agent by which they are respectively modified. In fewer 

 words, as long as heat preserves its own nature, the diversity of its 

 effects result, not from the analysis of its own constituents, but 

 from the superaddition of one common property to several proper- 

 ties. The relations of heat are various, but in an homogeneous 

 substance, or on one neither analysed nor divisible, it produces only 

 a single effect, which is to raise its temperature. As the question 

 concerning the ovum is, whether the properties in it, which are 

 subsequently to form the textures, are pre-disponent to, or identical 

 with, those properties which do form the textures, as this is the 

 present question, it appears that the argument cited in the last 

 paragraph is insufficient to decide it, because heat still retaining its 

 own nature, may supply to diversified pre-disponent properties of 

 the ovum that in which they are all deficient, in order to become 

 the identical ones of the textures. 



19> As the question is not determined by these facts, and as 

 its determination appears to be of some importance, it is proper to 

 recollect facts of another kind, which are also related with the 



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