6 INTRODUCTION TO CYTOLOGY 



Hugo von Mohl (1805-1872), in spite of his many valuable observa- 

 tions on the growth of algae, in 1835 agreed essentially with Mirbel. He 

 made a step in advance, however, when he described carefully for the 

 first time the division of a cell. We shall see further on that von Mohl's 

 later researches contributed largely to the upbuilding of an adequate 

 theory of the cell. 



F. J. F. Meyen (1804-1840) held that there are three fundamental 

 forms of elementary organs: cells, spiral tubes, and sap vessels. He 

 noted the wide occurrence of cell-division but did not describe the process 

 in detail. Meyen apparently made the first attempt to distinguish cell- 

 division from the free cell-formation described by previous workers. It 

 has been pointed out by Sachs that if this short step had been clearly 

 taken earlier the peculiar theory of cell-formation later developed by 

 Schleiden would have been impossible. Von Mohl also had made obser- 

 vations ruling out Schleiden's idea, but his excessive caution prevented 

 him from making a decisive statement on the subject. H. J. Dutrochet 

 (1776-1847) in 1837 described the body as being composed of solids and 

 fluids, the former being aggregations of cells of a certain degree of firmness, 

 and the latter, such as blood, being made up of cells freely floating. He 

 believed that although the cell contents may be more or less solid, the 

 highest degree of vitality is compatible only with the liquid condition. 

 He further recognized muscle fibers as elongated cells. 



To all the above workers the important elementary unit was the 

 "globule." It was customary to refer to this conception as the Globular 

 Theory, in contradistinction to the curious and fanciful Fiber Theory 

 put forth by Haller (1708-1777) many years before (1757), according to 

 which the organism is made up of slender fibers cemented together 

 by "organized concrete." For some the term "globule" stood for the 

 granules seen in the cell contents, whereas for others it meant the cell 

 itself. As observations multiplied and ideas became more definite the 

 Cell Theory of Schleiden and Schwann was more and more distinctly fore- 

 shadowed. Before turning to the Cell Theory, however, we must notice 

 briefly a few observations which had been made on the cell contents. 



Early Observations on the Cell Contents. Although the true nature 

 and significance of the contents of cells were not recognized until many 

 years later, a number of early investigators had seen protoplasm and had 

 been impressed by certain of its activities. As early as 1772 Corti, and a 

 few years later Fontana (1781) saw the rotation of the "sap" in the 

 Characeae and other plants. After being long forgotten these facts 

 were rediscovered by L. C. Treviranus (1811) and G. B. Amici (1819), 

 whereupon Horkel, an uncle of Schleiden, called attention to the earlier 

 work of Corti. Protoplasmic circulation of the more complex type was 

 discovered in the stamen hairs of Tradescantia by Robert Brown in 1831, 

 and other workers, especially Meyen, soon added other cases. 



