ORGANISMS ILLUSTRATING BlOL()(;i(;\| 



PRLNCIPLES 



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BEGINNINGS: THE LARGE CROIP OF THE 

 SMALLEST OHGA.MSMS 



Preview. Some forms found in a drop of fresh water: Ainoba. an 

 animal cell ; Euglena ; Paramecium ; Diatoms : Desmids ; Bacteria ■ Func- 

 tional differences between plant and animal cell • Suggested readings. 



PREVIEW 



Over two hundred and sixty years ago, when the Dutchman, Antony 

 van Leeuwenhoek, examined what he called "little animals" under 

 his homemade microscopes, he made the first real exploration of a 

 drop of water ever attempted. His microscopes were simple affairs, 

 consisting of a single lens. They had no tube or mirror such as our 

 microscopes of today have. When objects were examined they had 

 to be brought into position and focus through the use of rather coarse 

 screws. 



Besides being the first person actually to see the capillary circulation 

 of the blood (a thing that Harvey knew must be so, but which he wa.s 

 unable to prove), van Leeuwenhoek made numerous other llhJ^sio- 

 logical and anatomical observations which gave him the title of 

 "founder of histology." One thinks of him most often as the first 

 man who saw protozoa, unicellular plants, and own bacteria in 

 standing water. 



Let us read his own description and judge for ourseh-es a.s to what 

 he saw. The following extract is taken from a letter written on 

 October 9, 1676, to Henry Oldenburg, First Secretary of the Koyal 

 Society of London. It describes the finding of "little animals" in a 

 drop of rain water. 



"Of the first sort that I discovered in the said water, I saw, after divers 

 observations, that the bodies consisted of 5, 6, 7, or 8 ver>' clear globules, 

 but without being able to discern any membrane or skin that held these 

 globules together, or in which they were inclosed. When these aninuilcules 

 bestirred 'emselves, they sometimes stuck out two little hnrns, which were 

 continually moved, after tlie fashion of a horse's ears. The i)art l)etween 



H. W. H. — 11 131 



