A SPORE OF MILDEW. 



quite convinced that for a long while before the living par- 

 ticle which he is able to see acquired the size and substance 

 necessary to render it visible, it existed as a more minute 

 and more transparent yet active and living particle, capable 

 of growing and multiplying. The act of coming together 

 of the non-living molecules supposed, if it occurs at all, 

 must take place in particles so very very far beyond the 

 reach of observation and experiment, as to be quite un- 

 demonstrable. I believe the process, which some affirm to be 

 actually occurring at this time, is not conceivable. On the 

 other hand, the further investigation is carried by the 

 observer, the firmer becomes his conviction, that the most 

 minute individual particles he has seen have resulted from 

 the division and subdivision of already existing particles. 

 He sees the actual process of division taking place in hun- 

 dreds of instances, and in every class of living things, from 

 the very lowest up to man himself, and, in the absence of 

 positive demonstration to the contrary, he will feel unable 

 to admit that any other mode of origin of living organisms 

 of any kind whatever exists in nature. 



It must then be regarded as a fact that living beings 

 spring from pre-existing living beings, and that there is no 

 such thing as spontaneous generation. (See also remarks on 

 pp. 66, 176.) Living forms continue to exist and to grow so 

 long as the conditions of life remain favourable, but when 

 these are changed, the organisms languish or are killed. 



Of a Spore of Mildew. If one of the simple structures 

 the microscopic " protoplasms," such as are represented 

 in Plate I, fig. i at a, also in fig. 3, be examined, we shall 

 find that it is not the same in every part. It consists exter- 

 nally of a delicate, transparent, glass-like texture, and within 



o 



