Academy of Sciences in Paris. 561 



is observed in the capillary blood-vessels of dead animals ; this 

 trepidation of the molecules in the blood-vessels is not perceptible 

 under a diffused light, hut becomes visible when the vessels are ex- 

 posed to the action of the direct solar rays. The united testimony, 

 however, of the three academicians above mentioned was in opposi- 

 tion to M. Dutrochet's opinion, which they supposed to have origi 

 nated in his having only tried the experiments with the celandine, in 

 which the circulation is, in fact, not visible, except with direct light, 

 whereas, in the ficus elastica, alisma plantago, and others, it is 

 clearly to be distinguished by diffused light. 



This subject was resumed on the 28th of March, when M. Mirbel 

 read a letter from M. Amici, (well known for his improvements on 

 the microscope,) detailing some experiments which he had recently 

 made on the leaves of celandine, and which had induced him to 

 attribute the movement of the juice, not to a system of circulation, 

 but merely to the effect of the heat either of the lamp, or even, in 

 some cases, of the human hand alone. He conceives that the 

 caloric, acting on the gaseous molecules interspersed among the 

 solid or liquid molecules, occasions those molecules to dilate and 

 displace each other, thus forming a constant movement, which, 

 however real, he does riot admit to be circulation, as it is not de- 

 pendent on a vital principle ; or he supposes that the heat acts by 

 means of a thermo-electric current passing through the juices ; or, 

 thirdly, by means of the air passing from the trachea by the anasto- 

 mosis existing between the two orders of vessels, and thus impel- 

 ling the juice before it. But in order to remove any doubt as to the 

 effect being produced by the heat, and not by the light, M. Amici 

 subjected the leaves to the action of a hot iron, and perceived, by 

 the aid of a reflecting mirror, that the heat invariably determined 

 a motion of the fluid in an opposite direction, changing from left 

 to right, and vice versa, as the position of the iron was altered. 

 M. Amici thence concludes that celandine may be made useful as a 

 thermoscope. M. Mirbel, in remarking on this letter, observed 

 that, although some doubt may exist as to the reality of the circula- 

 tion in celandine, there can be none as to the ficus elastica, where 

 there is evidently not mere trepidation but translation visible by a 

 diffused light ; and that it is not determined by the influence of 

 caloric, as supposed by M. Amici with respect to celandine, is evi- 

 dent from the fact of the liquid passing in circulation under the 

 point exposed to the action of the direct solar rays, where the heat 

 is consequently greatest, and where, the action being vertical, the 

 supposed repellent power of the caloric ought to be neutralized, 

 and the liquid remain stationary in that point, and to be thence 

 repelled in opposite directions as from a centre, which is not the 

 case, the movement being uniformly in the same direction in each 

 vessel. M. Cassini also remarked that, if M. Amici were right in 

 his opinion, the phenomenon which he (M. Cassini) had observed 

 of two vessels containing the juice, and placed close together, ex- 

 hibiting a circulation in opposite directions, would be impossible. 

 M. Dutrochet also sent a second letter, in which he stated that he 



