178 THE FROG CHAP, x 



(Fig. 48) under the high power of the microscope, and 

 observe 



1. The nerve-cells, present in the grey matter only (com- 

 pare Fig. 54, A). Note their branched form and their 

 nuclei ; the larger motor cells are seen in the ventral horns 

 of the grey matter. Sketch. 



2. The nerve-fibres, in both grey and white matter, cut 

 across transversely as well as in other directions, and each 

 showing a deeply-stained central neuraxis. Sketch. 



b. Tease up a fresh spinal or sympathetic ganglion in salt 

 solution, and stain with methyl-green. Compare the form 

 of the nerve-cells with those in the spinal cord (Fig. 54, B). 

 Sketch. 



c. Cut off a very small piece of any fresh nerve (e.g. 

 sciatic), and tease it out carefully, in a longitudinal direction, 

 in salt solution. Note that it is made up of cylindrical, 

 unbranched nerve-fibres, bound together by connective- 

 tissue. 



Examine a single fibre under the high power (Fig. 54, A), 

 and make out the neurolemma, the medullary sheath, and the 

 nodes ; at the nodes, the neuraxis can also be seen. Sketch. 



Tease out another piece of fresh nerve in chloroform, so as 

 partially to dissolve the medullary sheath, and note the 

 central neuraxis. Sketch. 



Tease out in glycerine a piece of nerve which has been 

 treated with a i per cent, solution of osmic acid in water for 

 an hour or two and then well washed in water. The 

 medullary sheath will appear nearly black, and the neuro- 

 lemma, as well as the nodes, can be plainly seen. Sketch. 



Reflex Action. The experiment described on p. 169 

 should be seen. 



