HISTORICAL SKETCH 5 



Early Theories of Cell-formation. The researches of Hooke, 

 Malpighi, and Grew in the seventeenth century had shown that "cells," 

 or "globules," are important structural elements in organisms. When 

 attention was again directed to such matters in the eighteenth century 

 there .was very soon felt a need for a theory which would account for the 

 origin of cells. We may briefly review some of the suggestions which were 

 offered. 



One of the earliest theories of cell-formation was that put forward by 

 Wolff in the Theoria Generationis. According to Wolff, every organ is 

 at first a clear, viscous fluid with no definite structural organization. 

 In this fluid cavities (Blaschen; Zellen) arise and become cells, or, by 

 elongation, vessels. These may later be thickened by deposits from the 

 " solidescible " nutritive fluid. The cavities, or cells, are not to be 

 regarded as independent entities ; organization is not effected by them, 

 but they are rather the passive results of an organizing force (vis essen- 

 tialis) inherent in the living mass. Three important points in Wolff's 

 theory should be noted because of the relation they bear to subsequent 

 conceptions of the role of cells: the spontaneous origin of the cell, the 

 organization of parts by differentiation in a homogeneous living mass, 

 and the passive role of the cell in this organizing process. This theory 

 was adopted in 1801 by C. F. Mirbel (1776-1854), who further believed 

 that the cells communicate through pores in their walls. 



K. Sprengel (1766-1833) stated that cells originate in the contents 

 of other cells as granules or vesicles which absorb water and enlarge. 

 Sprengel's observations seem to have been very poorly made, for he 

 evidently mistook starch grains for the "vesicles" which were supposed 

 to grow into new cells. But Sprengel's theory was upheld by L. C. 

 Treviranus (1779-1864) in a work appearing in 1806, and both men fought 

 many years for its support. Kieser (1812) further developed the theory 

 that granules in the latex are "cell germs" which later hatch in the inter- 

 cellular spaces to form new cells. 



With a much clearer understanding of the nature of the problems 

 involved a number of excellent observations were made by J. J. Bern- 

 hardi in 1805, by H. F. Link and K. A. Rudolphi in 1807, and by J. J. P. 

 Moldenhawer in 1812. It is to be regretted that the deserved attention 

 was not given to their views, for they promised to lead in the right 

 direction. 



A number of years later Mirbel, in a work on Marchantia (183 1-1833), 

 distinguished three modes of cell-formation: (1) the formation of cells on 

 the surface of other cells, (2) the formation of cells within older cells, and 

 (3) the formation of cells between older cells. The first mode apparently 

 represented the budding of the germ tube arising from the spore, while the 

 second and third modes were formulated as the result of a misinterprets 

 tion of the process of cell-multiplication in growing gemmae. 



