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Additional Remarks un Active Molecules. By Robert Brown, 



F. R. S. &c. 

 About twelve months ago I printed an account ot" Microscopi- 

 cal Observations made in the summer of 1827, on the Par- 

 ticles contained in the Pollen of Plants; and on the general 

 Existence of active Molecules in Organic and Inorganic Bodies. 



In the present supplement to that account, my objects are, to 

 explain and modify a few of its statements, to advert to some of 

 the remarks that have been made, either on the correctness or 

 originality of the observations, and to the causes that have been 

 considered sufficient for the explanation of the phenomena. 



In the first place, I have to notice an erroneous assertion of 

 more than one writer, namely, that I have stated the active 

 molecules to be animated This mistake has probably arisen 

 from my having communicated the facts in the same order in 

 which they occurred, accompanied by the views which presented 

 themselves in the different stages of the investigation ; and in 

 one case, from my having adopted the language, in referring to 

 the opinion of another inquirer into the first branch of the sub- 

 ject. 



Although I endeavoured strictly to confine myself to the 

 statement of facts observed, yet in speaking of the active mole- 

 cules I have not been able, in all cases, to avoid the introduc- 

 tion of hypothesis ; for such is the supposition, that the ecjually 

 active particles of greater size, and frequently of very different 

 form, are primary compounds of these molecules, — a supposi- 

 tion which, though professedly conjectural, I regret havino- so 

 much insisted on, especially as it may seem connected with the 

 opinion of the absolute identity of the molecules, from what- 

 ever source derived. 



On this latter subject, the only two points that I endeavour- 

 ed to ascertain, were their size and figure : and although I was, 

 upon the whole, inclined to think that in these respects the 

 molecules were similar from whatever substances obtained, yet 

 the evidence then adduced in support of the supposition was far 

 from satisfactory ; and I may add, that I am still less satisfied 

 now that such is the; fact. But even had the uniformity of the 

 molecules in those two points been absolutely established, if did 



