50 WENHAM, ON THE SAP-CIRCULATION OF PLANTS. 



Lest it should be imagined, that I advocate the long-ex- 

 ploded theory, that supposed all vitality to originate with 

 active molecules, I will venture, in conclusion, to make a few 

 brief remarks in relation to them. The existence of active 

 molecules has been known in a very early age of the micro- 

 scope, but the first definite information on the subject, was 

 given in the paper of Dr. Robert Brown, published in the 

 ' Edinburgh Journal of Science,' for July, 1828. These 

 observations rather tended to favour the above theory than 

 otherwise, from the circumstance of his connecting together, 

 without due distinction, both inorganic and organic molecules, 

 some of the latter being obtained from actual living plants. 

 The difference between vital and inorganic molecules is im- 

 mediately perceptible, when submitted to the action of proper 

 tests. Active molecules may be obtained froin very many 

 different mineral and inorganic bodies, as sulphur, limestone- 

 rock, ashes, and even burnt clay. Their motions have been 

 successively attributed to the influence of mutual attraction, 

 caloric, and electricity ; I have tried several experiments upon 

 them with these two agents, but without obtaining definite 

 results ; nor am I yet satisfied with any explanation that has 

 hitherto been given of the cause of their activity. I merely 

 mention this in order to show the very wide difference exist- 

 ing between these and the active molecules, or rather cor- 

 puscles, contained in the vegetable cell ; to all appearance 

 their movements are identical, but the motion of the latter 

 may be entirely suspended, or awakened, by the range of 

 temperature consequent upon ordinary atmospheric changes. 

 Their vital activity is immediately destroyed by a small trace 

 of hydrochloric or sulphuric acid. The motion is increased by 

 the agency of a slightly-alkaline solution, particularly that of 

 ammonia ; but this stimulant added to excess becomes a 

 poison, and destroys the principle of activity.* 



On the other hand, active molecules obtained from a pow- 

 dered brick-bat, for example, may be exposed to considerable 

 differences of temperature, without their motions being 

 affected by it ; and provided there is no chemical decom- 

 position, they exhibit the same degree of energy, whether the 

 solution be either acid or alkaline. 



* A fact curiously in accord with what has been observed by KoUiker, 

 with respect to the action of the same re-agents upon the spermatic fila- 

 ments of animals. — Vide ' Quarterly Journal of Microscopical Science,' 

 vol. iii., p. 293.— [Eds.] 



