STRUCTURE OF A SPORE OF MILDEW. 75 



for believing that the most minute individual particles he sees 

 resulted from the division and subdivision of already existing 

 particles. He sees the actual process of division taking place 

 in hundreds 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 cannot 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. Living forms con- 

 tinue to exist and to grow so long as the conditions of life 

 remain favourable, but when these are changed, the or- 

 ganisms die. 



Structure of a Spore of Mildew. If one of the simple 

 structures the microscopic protoplasms such as are repre- 

 sented in the plate opposite p. i, be examined (a), we shall 

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

 externally of a delicate, transparent, glass-like texture, and 

 within of a material having a faintly granular appearance. 

 Suppose a little ordinary mildew dust, which is one of the 

 lowest forms of existence possessing a very simple structure 

 be examined. The little round bodies which compose it 

 are larger than those above referred to, and will therefore 

 suit the purpose of investigation better. Each of these has 

 a tolerably thick well-defined outline, while the interior is 

 perfectly transparent. When this transparent matter is ex- 

 amined under very high magnifying powers, numerous very 

 minute particles like dots will be observed. Here then are 

 two parts, the one situated externally, firm, glass like, and 



