1870.] BRITISH ASSOCIATION. 325 



by the aid of the microscope ; while a large proportion belong to 

 the category of smallest things of which I have spoken, and which 

 must have all looked like mere dots and lines under the ordinary 

 microscopes of the eighteenth century. 



Led by various theoretical consideratioos, which I cannot now 

 discuss, but which looked promising enough in the lights of that 

 day, Buifon and Needham doubted the applicability of Redi's 

 hypothesis to the infusorial animalcules, and Needham very 

 properly endeavoured to put the question to an experimental test. 

 He said to himself, if these infusorial animalcules come from 

 germs, their germs must exist either in the substance infused, 

 or in the water with which the infusion is made, or in the 

 superjacent air. Now the vitality of all germs is destroyed by 

 heat. Therefore, if I boil the infusion, cork it up carefully, 

 cementing the cork over with mastic, and then heat the whole 

 vessel by heaping hot ashes over it, 1 must needs kill whatever 

 germs are present. Consequently, if Redi's hypothesis hold 

 good, when the infusion is taken away and allowed to cool, no 

 animalcules ought to be developed in it ; whereas, if the 

 animalcules are not dependent on pre-existing germs, but are 

 generated from the infused substance, they ought, by-and-by, to 

 make their appearance. Needham found that, under the 

 circumstances in which he made his experiments, animalcules 

 always did arise in the infusions, when a sufficient time had 

 elapsed to allow for their developement. 



In much of his work Needham was associated with BufFon, and 

 the results of their experiments fitted in admirably with the great 

 French naturalist's hypothesis of '* organic molecules," according to 

 which, life is the indefeasible property of certain indestructible 

 molecules of matter, which exist in all living things, and have 

 inherent activities by which they are distinguished from not 

 living matter. Each individual living organism is formed by 

 their temporary combination. They stand to it in the relation of 

 the particles of water to a cascade or whirlpool ; or to a mould, 

 into which the water is poured. The form of the organism is 

 thus determined by the reaction between external conditions 

 and the inherent activities of the organic molecules of which it is 

 composed ; and, as the stoppage of a whirlpool destroys nothing 

 but a form, and leaves the molecules of the water, with all their 

 inherent activities intact, so what we call the death and 



