486 Mr. J. D. Dana on Species. 



specific amount or law of force ; and we even set down in num- 

 bers the precise value of this force as regards one of the deepest 

 of its qualities, chemical attraction. Taking the lightest element 

 as a unit to measure others by, as to their weights in combination, 

 oxygen stands in our books as 8 ; and it is precisely of this nu- 

 merical value in its compounds : each molecule is an 8 in its 

 chemical force or law, or some simple multiple of it. In the 

 same way there is a specific number at the basis of other quali- 

 ties. Whenever then the oxygen amount and kind of force was 

 concentered in a molecule, in the act of creation, the species 

 oxygen commenced to exist. And the making of many such 

 molecules instead of one, was only a repetition in each molecule, 

 of the idea of oxygen. 



In combinations of the elements, as of oxygen and hydrogen, 

 the resultant molecule is still equivalent to a fixed amount, 

 condition, or law, of chemical force ; and this law, which we ex- 

 press in numbers, is at the basis of our notion of the new species. 



It is not necessarily a different amount of force ; for it may 

 be simply a different state of concentration or different rate or 

 law of action. This should be kept in mind in connexion with 

 what follows *. 



The essential idea of a species, thence deduced, is this : a spe- 

 cies corresponds to a specific amount or condition of concentered 

 forcCy defined in the act or law of creation. 



Turn now to the organic world. The individual is involved 

 in the germ- cell from which it proceeds. That cell possesses 

 certain inherent qualities or powers, bearing a definite relation 

 to external nature, so that, when having its appropriate nidus or 

 surrounding conditions, it will grow, and develope out each organ 

 and member to the completed result, and this, both as to all 

 chemical changes, and the evolution of the structure which be- 

 longs to it as a subordinate to some kingdom, class, order, genus 

 and species in nature. The germ-cell of an organic being de- 

 velopes a specific result ; and like the molecule of oxygen, it must 

 correspond to a measured quota or specific law of force. AVe 

 cannot apply the measure, as in the inorganic kingdom, for we 

 have learned no method or unit of comparison. But it must 

 nevertheless be true, that a specific predetermined amount, or 



* When we have in view oxygen and the elements, we are apt to think 

 of their molecules as distinguished by a diflferent amount and kind of force. 

 But when we consider the many diflPerent compounds that may be made of 

 the same elements (as carbon and hydrogen), in the very same proportions, 

 we are led to conceive of these as differing molecularly in a different law 

 of the same force or forces. When, again, we see the same element under 

 conditions as diverse as any two compounds, as in cases of allotropism, we 

 are still better satisfied with adopting, for the present, the most general 

 expression — a different law of action or condition of molecular force. 



I 



