CHAPTER III 

 MODEL MAKING 



Lord Kelvin said, "Can ye make a model of it? For if ye can, 

 ye understand it, and if ye canna, ye dinna!" This remark 

 epitomizes the philosophy of science in Mid- Victorian days. 

 There is much to be said in favor of visualizing an idea by making 

 a mental, if not an actual, working model of it, but a model is by 

 no means necessary in order to comprehend an idea; and, on the 

 other hand, while a model may greatly elucidate an idea, it may 

 also obscure it and lead to a wholly erroneous conclusion. The 

 fact that the model works very well and does precisely what it is 

 intended to do is not evidence that the mechanism which it is 

 supposed to imitate also works that way. There was once 

 constructed a model intended to show how the contractile vacuole 

 of a protozoan operates. The model contained valves and numer- 

 ous other appliances. It worked and did what the contractile 

 vacuole does, but few would go so far as to say that a contractile 

 vacuole contains mechanical devices such as the model contained 

 or anything like them. 



Model making in biology includes any attempt to imitate vital 

 phenomena with nonliving material. It is more extensively 

 practiced than one, on first thought, realizes. The experiments 

 of Biitschli, in which he produced structure in gels similar to those 

 in protoplasm; the experiments of Rhumbler, in which the move- 

 ments of liquid drops of mercury were observed with the hope 

 that they would throw some light on the mechanism of amoeboid 

 movement; and the experiments of R. Lillie with iron wire 

 immersed in solution, imitating the action of nerves, are all 

 experiments in model making. 



A number of common laboratory procedures imitate happen- 

 ings in the living world accurately in principle, without, however, 

 reproducing the vital processes exactly as to material and form. 

 Osmotic cells made in the laboratory function just as do plant 

 cells, even though in construction or material they differ from 



the living cell. 



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