174 THE CELL-THEORY 



logical turn of mind. Schwann was only twenty-nine when 

 his master-work appeared, and the book is clearly the work 

 of a young man. It has the clear structure, the logical finish, 

 which the energy of youth imparts to its chosen work. So 

 the work of Rathke's prime, the Anatotnische-philosophische 

 Untersuchungen of 1832 shows more vigour and a more 

 reasoned structure than his later papers. Schwann's book is 

 indeed a model of construction and cumulative argument, 

 and even for this reason alone justly deserves to rank as 

 a classic. 



The first section of his book is devoted to a detailed 

 study of the structure and development of cartilage cells and 

 of the cells of the notochord, and to a comparison of these 

 with plant cells. He accepts Schleiden's account of the 

 origin and development of nuclei and cells as a standard 

 of comparison ; and he seeks to show that nucleus and 

 nucleolus, cell-wall and cell-contents, show the same relations 

 and behave in the same manner in these two types of animal 

 cells as in the plant-cells studied by Schleiden. The types 

 of cell which he chose for this comparison are the most plant- 

 like of all animal cells, and he was even able to point to a 

 thickening of the cell-wall in certain cartilage cells, analogous 

 to the thickening which plays so important a part in the 

 outward modification of plant-cells. The analogy indeed in 

 structure and development between chorda and cartilage 

 cells and the cells of plants seemed to him complete. The 

 substance of the notochord consisted of polyhedral cells 

 having attached to their wall an oval disc similar in all 

 respects to the nucleus of the plant-cell, and like it containing 

 one or more nucleoli. Inside the mother-cell were to be 

 found young developing cells of spherical shape, lacking 

 however a nucleus. Cartilage was even more like plant 

 tissue. It was composed of cells, each with its cell membrane. 

 The cells lay close to one another, separated only by their 

 thickened cell-wall and the intercellular matrix, showing thus 

 even the general appearance of the cellular tissue of plants. 

 They contained a nucleus with one or two nucleoli, and the 

 nucleus was often resorbecl, as in plants, when the cell 

 reached its full development. Other nuclei were in many 

 cases present in the cell, round which young cells could be 



