CELLS AS IMBIBITION-CRYSTALS 185 



formed substance may remain in solution in the cytoblastem 

 or may crystallise out as the beginning of a new cell ; another 

 part, the cell-substance, crystallises round the nucleolus. 

 The cell-substance is either soluble in the cytoblastem and 

 crystallises out only when the latter is saturated with it, or it 

 is insoluble and crystallises as soon as it is formed, according 

 to the aforementioned laws of the crystallisation of imbibition- 

 bodies ; it forms thus one or more layers round the nucleolus, 

 etc. If one imagines cell-formation to take place in this 

 way, one is led to think of the plastic force of the cell as 

 identical with the force by means of which a crystal grows " 



(PP- 249-50). 



Two difficulties have to be faced by this theory (i) the 

 origin of the metabolic power of the cells, (2) the reason why 

 the cells arrange themselves so as to form an organism of 

 complex and definite structure. Schwann tries to explain the 

 origin of the " metabolic " action, the analogy of which with 

 the contact-action of colloidal platinum he recognises, by 

 attributing it to the peculiar structural arrangements of 

 molecules. In attempting to account for the harmonious 

 structure of the organism he points to the analogy of ordinary 

 crystals, which often form complex and regular tree-like 

 arrangements ; plants in particular resemble these regularly 

 shaped crystal-aggregates. 



The whole ingenious theory is offered merely as an 

 hypothesis and a guide to research. It is interesting as one 

 of the most carefully thought-out attempts ever made tp give 

 a thorough-going materialistic account of the origin and 

 development of organic form, and it arose directly out of the 

 cell-theory. 



Schleiden and Schwann started out from an erroneous 

 theory of the origin and development of cells, which impaired 

 to some extent the value of their results. It was not long, 

 however, before their theory of the origin of cells by 

 " crystallisation " from an intra- or extra-cellular cytoblastem 

 was challenged and overthrown, and the generalisation that 

 cells originate by division from pre-existing cells put in its 

 place. 



This was established for plant cells by Meyen, Unger, 

 von Mohl, Naegeli and Hofmeister in or about the 



