ORIGIN OF SPECIES. 37 



which does not have recourse to laws with which we are as 

 yet unacquainted. Thus, it is not at variance with any known 

 law to suppose that the primary molecules are the result of 

 the development of germs which find in the inorganic infusion 

 a suitable nidus ; that these primary molecules and the vibrios 

 which they produce are referable to the Protophyta, and 

 should probably be placed near the filamentous Confervas ; 

 that by the death of these vegetable organisms the fluid is 

 prepared for the reception and development of the germs of 

 the Protozoa, for which the former serve as pabulum; and 

 that many of the forms which are observed are the larval 

 stages of the higher Infusoria.* 



13. ORIGIN OF SPECIES. 



It is impossible here to do more than merely indicate in the 

 briefest manner the two fundamental ideas which are at the 

 bottom of all the various theories as to the origin of species. 

 The opinions of scientific men are still divided upon this sub- 

 ject ; and it will be sufficient to give an outline of the two 

 leading theories, without adducing any of the reasoning upon 

 which they are based. 



I. Doctrine of Special Creation. On this doctrine of the 

 origin of species it is believed that species are immutable pro- 

 ductions, each of which has been specially created at some 

 point within the area in which we now find it, to meet the 



* Recent researches, especially those of Dr Bastian, have established 

 some new facts as to the possibility of Heterogeny, but they can by no 

 means be said to .have settled the question, if only upon the ground that 

 they require confirmation by other experimentalists. The chief fact which 

 appears to have been established upon a tolerably firm basis is, that living 

 beings, vegetable or animal, may make their appearance in organic infu- 

 sions which have been subjected to a temperature of considerably over 

 the boiling-point, even though the said infusions have been hermetically 

 sealed in a flask from which all atmospheric air has been previously with- 

 drawn. The chief deduction which appears to flow from this assuming 

 its correctness is, that there are low organisms which can exist, for a 

 certain length of time at any rate, with an extremely small amount of air ; 

 for it is to be remembered that the production of a theoretically perfect 

 vacuum is probably practically impossible. If it were conceded, in fact, 

 that a perfect vacuum had been formed in the experiments in question, the 

 sole result would be that we should have to alter all our beliefs as to the 

 conditions under which life is a possibility. The only tangible result of 

 these experiments, so far, is, that any supposed " pre-existent germs" must 

 have been contained, if present at all, in the infinitesimal portion of 

 air which could not be expelled from the flasks experimented on ; or, they 

 must have been able to withstand without injury a temperature of over 

 212. Neither of these hypotheses is wholly incredible ; but the question 

 ought to be regarded as still sub judice. 



