THE president's ADDRESS. 361 



inclined to think that the only known forms of life which would 

 be capable of such migration are some of the various kinds of 

 "filter-passers," with regard to which our knowledge is slowly 

 increasing, though still very incomplete namely, those minute 

 forms of life, some of them apparently beyond the range of vision 

 of our highest powers of the microscope, which pass through the 

 bacterial filters. I have dealt with examples of such forms in 

 the case of the so-called Chlamydozoa. 



The question arises at this point, what is the size approximately 

 of the smallest bodies that can be seen with our microscopes ? 

 I hesitate, before an audience of experts, to pronounce a decided 

 opinion on this point, but I believe that with the best powers of 

 the microscope at present available a body measuring 0'1/x, (o-twoo 

 of an inch) would be just visible, if it were differentiated optically 

 in some way, by staining or refringence, from its surroundings. 

 This is considerably less than the limit of size required by the 

 Arrhenian theory, and an invisible, filter-passing organism 

 would certain 1}' be small enough to be transported by radiation 

 pressure. 



So far, then, the Arrhenian theory supports the view that I 

 have put forward above namely, that the most primitive form of 

 life was a minute speck of substance of the nature of chromatin, 

 since any cytoplasmic organisms known to us, of the type of an 

 amoeba, for example, would be much too large to be propelled by 

 radiation-pressure in space. 



In contrast also with the Lankesterian theory, the Arrhenian 

 theory rests on a purely vitalistic basis namely, on the assump- 

 tion that living things are fundamentally different in their 

 nature and properties from those that are not living. No 

 generation of the living from the lifeless took place, according to 

 Arrhenius, at any period to which we can throw our thoughts 

 back ; if it took place at all, it must have been at a period 

 during or before the beginning of the material universe as we 

 know it. Life carries on its characteristic activities subject to, 

 and restrained by, the physico-chemical laws of matter, but does 

 not owe its origin to those laws, and is not perhaps, in other 

 worlds, bound up with the same forms of matter with which it is 

 connected in ours. The minute chromatin-particle or germ of 

 life might conceivably, on another planet, set in motion vortices 

 of metabolic change quite different from that type with which 



