216 president's address. 



back lens for the same or even a lower power ? Clearly it 

 traverses the wliole genius and meaning of the diffraction 

 theory. It was only in pre-apochromatic days that such 

 attempts as these could be made. 



Now, in the new era of objectives, we do not seek for any 

 purpose to transcend the society screw, and the apertures 

 easily obtained within the limits of that screw, viz., 0'3 for an 

 inch and 0*65 for a half-inch objective, represent with high 

 probability the greatest ratios of apertures to power that will 

 be produced for many years. 



Clearly, then, there must be some egregious oversight in 

 commending greater back lenses than the society screw will 

 admit of in the 3'ear 1893, and to an audience receiving instruc- 

 tion in the paramount value of the diffraction theory of 

 microscopic vision. 



Turning now, however, to work done by means of the 

 microscope rather than to the instrument itself, a matter of 

 much interest call^ for our unbiassed hearing. 



It has, doubtless, been known for some time to the members 

 of this Club that Prof. 0. Biitschli has been engaged in efforts 

 at an experimental imitation of protoplasm. These experiments 

 are not of an elaborate chemical order, carrying us into the 

 profounds of organic chemistry. By means of quite another 

 kind the great problem is approached : the experiments are of 

 the simplest order, needing only supreme accuracy and care ; 

 and after ten j^ears of research work we are furnished with the 

 results.* 



Of course it will be remembered that the absolute uniqueness 

 of protoplasm as the only known seat or centre for the properties 

 of life has been maintained for the last twenty years by the 

 leading biologists of the world. Thus Prof. Huxley affirmsf 

 that the " properties of living matter distinguish it absolutely 

 from all other kinds of things, and the present state of our 

 knowledge furnishes us with no link between the living and 

 the not living." 



But it may be fairly affirmed that if, by experimental 

 methods and careful research, it could be shown that proto- 



* " Untersuchnngen ueber Mikroskopische Schaeume and das Proto- 

 plasma." By O. Butschli. Leipzig, EnglemanD, 1892. 

 t " Ency. Brit.," Vol. iii., p. 679, 9th ed. 



