54 Wisconsin Academy of Sciences, Arts and Letters. 



How does this increase in number of fibres take place? It 

 may come either by division of fibres previously present, or 

 by new formation. The latter method is on all grounds more 

 probable. The relative size of fibres in young and old frogs 

 forbids us to think of division as the process, since in young- 

 frogs the fibres are of far smaller average size. This is 

 shown by the number of fibres which stand in a given area, 

 as the following table exhibits : 



I 



Hence the fibres in the smallest frog had hardly one-third 

 the area of those in the larger frog. The large fibres in both 

 are about the same size, but there are in the smaller frogs a 

 vast number of minute fibres. There are also, probably, 

 others not yet medullated and hence not rendered visible by 

 osmic acid, which develop into the new nerve fibres of the 

 older frogs. 



The size of the fibres is by no means the same in the dif- 

 ferent nerves of the same frog as the following table will 



show: 



TABLE IV. 



Frog No. 36 — "Wt. 63 grm. 



The differences are obvious, and unquestionably depend 

 on tbe function of the nerves. The first three nerves, which 

 supply the tongue,' forward extremity, etc., have an area of 



