CHAPTER VII 



MICROSCOPY AND CYTOLOGY 



Improvement of the microscope 



As HAS BEEN PREVIOUSLY POINTED OUT, microscopical rcseafch had a pe- 

 riod of brilliant success in the seventeenth century, the age of Mal- 

 L pighi and Leeuwenhoek. Afterwards, however, this method made 

 no further advance for more than a hundred years; the eighteenth century 

 certainly produced some microscopists of importance, such as, for instance, 

 Lieberkiihn, but on the whole little was achieved during this period with 

 the aid of magnifying apparatus. The reason for this was that the aforesaid 

 scientists of the seventeenth century and their contemporaries did all that 

 could be done with the instruments at their disposal; microscopes were and 

 remained imperfect, and improvements were a long time in coming. The most 

 serious difficulty lay in the chromatic aberration of the lenses; a colourless 

 object seen under the microscope would shimmer with all the colours of the 

 rainbow, a fact which naturally gave rise to countless misinterpretations of 

 the objects investigated. To procure achromatic glass, free from this fault, 

 was a task that occupied many scientists at that time; Newton himself de- 

 clared the problem to be insoluble. Eventually a Swede, Samuel Klingen- 

 STIERNA (1698-1765), professor of physics at Upsala, succeeded in working 

 out how the achromatic glass should be made, and under his instructions an 

 English mechanician, Dollond, constructed the first achromatic lenses. It 

 was some time, however, before the invention could be utilized for microscop- 

 ical purposes. Among those who in the beginning of the nineteenth century 

 constructed microscopes with achromatic lenses may be mentioned the 

 Frenchman Chevalier and the Italian Amici; the latter's microscopes in 

 particular were very fine, and there soon arose in every country microscope- 

 makers who produced gradually perfected instruments. The year 1817 is 

 named as that in which Amici demonstrated his first achromatic lens-sys- 

 tem and during the thirties the biological institutions, at least the more im- 

 portant ones, were able to obtain specimens of these improved microscopes. 

 It was at the beginning of that decade also that microscopical biology first 

 showed any notable advance, and after that the great discoveries in this field 

 followed one another in rapid succession. 



There were two spheres in which the pioneers of the new method were 

 induced to try their strength; on the one hand, the structure of the higher 



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