CHAPTER I 



HISTORICAL SKETCH 



The history of cytology falls naturally into three periods, of which 

 the first begins with the discovery of the cell by Robert Hooke in 1665, 

 the second with the foundation of the Cell Theory by Schleiden and 

 Schwann in 1838-9, and the third with the important researches of 

 Strasburger, Hertwig, Biitschli, and others between 1870 and 1880. In 

 the present sketch attention will be confined almost entirely to the first 

 two periods, the work of the third, or modern, period being dealt with in 

 the other chapters of the book. 



Prior to the seventeenth century attempts to analyse the structure 

 of organisms were necessarily unsatisfactory. Aristotle (384-322 B.C.) 

 in his De Partibus Animalium distinguished the "homogeneous parts" 

 and the "heterogeneous parts," the former corresponding in general to 

 what we classify as tissues (bone, fat, cartilage, flesh, blood, lymph, 

 nerve, membrane, nails, hair, skin, vessels, tendon, etc.), and the latter 

 being the larger members of the body (head, face, hands, feet, trunk, 

 etc.). Theophrastus, the pupil and successor of Aristotle, taught in his 

 Historia Plantarum that the plant body is composed of "sap," "veins," 

 and "flesh." Aristotle's classification was developed further by Galen 

 (131-201 A.D.) and by his followers. Although we no longer regard the 

 above components as elementary parts, but rather as tissues and organs, 

 the ancients may be pardoned for not carrying the analysis further, for they 

 did not possess the necessary instruments. Something was then known 

 about the refraction of light, but it was not until many centuries later 

 that suitable lenses were available. The first compound microscope was 

 brought out in 1590 by J. and Z. Janssen, spectacle makers of Middle- 

 burg, Holland; and during the first part of the seventeenth century 

 other improved models were designed by other workers. These instru- 

 ments in the hands of men possessed of scientific curiosity soon led to 

 many significant discoveries. A new world was opened to the eye of 

 science, and the compound microscope has since remained an instru- 

 ment of extraordinary value in biological research. 



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