644 THE FORMS OF TISSUES [ch. viii 



made up of simple, or simpKfied, cases of phenomena which in their 

 actual and concrete manifestations are usually too complex for 

 matheniatical analysis; hence, even in physics, the full mechanical 

 explanation of a phenomenon is seldom if ever more than the 

 ''cadre ideal" towards which our never-finished picture extends. 

 When we attempt to apply the same methods of mathematical 

 physics to our biological and histological phenomena, we need 

 not wonder if we be Hmited to illustrations of a simple kind, 

 which cover but a small part of the phenomena with which 

 histology has to do. But yet it is only relatively that these pheno- 

 mena to which we have found the method appUcable are to be 

 deemed simple and few.. They go already far beyond the simplest 

 phenomena of all, such as we see in the dividing Protococcus, and 

 in the first stages, two-celled or four-celled, of the segmenting egg., 

 They carry us into stages where the cells are already numerous, 

 and where the whole conformation has become by no means easy 

 to depict or visuahse, without the help and guidance which the 

 phenomena of surface-tension, the laws of equihbrium and the 

 principle of minimal areas are at hand to supply. And so far as 

 we have gone, and so far as we can discern, we see no sign of the 

 guiding principles faihng us, or of the simple laws ceasing to hold 

 good. 



