98 M. RaspaiPs experiments on the granules of Pollen. 



grains of fecula, at the instant they reach the water, perform 

 the part of infusory animalcuh, and the grains of pollen them- 

 selves then execute motions of recoil sufficiently picturesque up 

 to the very moment of explosion. 



3d, The evaporation of the water which supports the granvr- 

 les. — As the evaporation causes the level of the different 

 points of fluids to vary every instant, it is evident that the gra- 

 nules floating on the surface must from this cause appear to 

 approach or to retire spontaneously. It is also remarked that 

 the motions of inactive bodies when observed in the microscope, 

 will be always in the direct ratio of the elevation of tempera- 

 ture. An idea may be formed a little exaggerated of the 

 eff*ects of a similar cause, by placing in the focus of a micro- 

 scope the inactive granules in a drop of diluted alcohol. 



4ith, The evaporation of the volatile substances with which the 

 granules in issuing from pollen may be impregnated. — These 

 substances exist in the pollen in great abundance, as analysis de- 

 monstrates. The bodies which issue during the explosion ought 

 to be impregnated with them ; but the evaporation of a volatile 

 substance which covers an inert body, ought evidently to im- 

 press upon the latter the most illusory movements. In order 

 to be convinced of this, we have only to throw into the water 

 of the object-plate, grains of fecula previously moistened with 

 ether or alcohol. 



5^/*, The ordinary motions of great tozvns. — In a populous 

 city it is hardly possible to make a single microscopic obser- 

 vation, without remarking a sort of shaking occasioned by the 

 rolling of the carriages. 



6th, The motions caused by the agitation of the air. — This 

 cause varies according to the currents ; it exists sometimes with- 

 out the knowledge of the observer, and even when he does not 

 suspect there is the least agitation in the atmosphere. It is 

 sufficient for this that the current of air be only at the level of 

 the object-plate. Even the breathing of the observer renders 

 the effects still more intense. 



7f A, The motions caused by the hands of the observer, occupied 

 in drawing or leaning upon the table. — This cause of agitation 

 is so powerful, that it is easy to count with the microscope the 

 arterial j^ulsations. 



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