A HISTORY OF SCIENCE 



of the nineteenth century rushed as eagerly into the 

 new realm of the microscope as, for example, their suc- 

 cessors of to-day are exploring the realm of the X-ray. 



Lister himself, who had become an eager interro- 

 gator of the instrument he had perfected, made many 

 important discoveries, the most notable being his final 

 settlement of the long-mooted question as to the true 

 form of the red corpuscles of the human blood. In 

 reality, as everybody knows nowadays, these are bicon- 

 cave disks, but owing to their peculiar figure it is easily 

 possible to misinterpret the appearances they present 

 when seen through a poor lens, and though Dr. Thomas 

 Young and various other observers had come very near 

 the truth regarding them, unanimity of opinion was 

 possible only after the verdict of the perfected micro- 

 scope was given. 



These blood corpuscles are so infinitesimal in size that 

 something like five millions of them are found in each 

 cubic millimetre of the blood, yet they are isolated par- 

 ticles, each having, so to speak, its own personality. 

 This, of course, had been known to microscopists since 

 the days of the earliest lenses. It had been noticed, 

 too, by here and there an observer, that certain of the 

 solid tissues seemed to present something of a granular 

 texture, as if they, too, in their ultimate constitution, 

 were made up of particles. And now, as better and 

 better lenses were constructed, this idea gained ground 

 constantly, though for a time no one saw its full signifi- 

 cance. In the case of vegetable tissues, indeed, the 

 fact that little particles encased in a membranous cov- 

 ering, and called cells, are the ultimate visible units of 

 structure had long been known. But it was supposed 



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