138 ELEMENTARY BIOLOGY. [CHAl 



C. Schmidfs nodes. Examine the medullai 

 sheath of the least distorted fibres with grea^ 

 care ; the above will be found as interruptions 

 of the same at short and fairly regular inj 

 tervals, the sheath appearing to consist of 

 series of imbricated segments. 



t]. Compare a fibre with irregular contour. Not( 

 that the irregularity is due to shrinking ox 

 the medullary sheath under coagulation. The 

 coagulate masses may often be seen to cor- 

 respond with the above-named segments. 



iii. Tease up a piece of the trunk of a spinal nerve 

 in a drop of i per cent, osmic acid solu. After 

 3 — 4 hours immersion in the same, wash well 

 and mount in weak glycerine. Examine under 

 a high power. 



a. The medullary sheath ; rendered blackish and 

 highly conspicuous by the above metho( 

 Examine it with care, noting especially th|| 

 nodes of Ranvier and Schmidt. 



p. The axis fibre ; greyish ' and well defined; 

 seen on focussing through a. 



The nerve corpuscles ; apparent as thickeningi 

 of the sheath which bulge inwards, usually 

 of a reddish brown colour under treatment 

 with the above acid. They correspond in 

 number with the nodes of Ranvier, and each 

 consists of an oval refractive nucleus, em- 

 bedded in a small amount of granular proto- 

 plasm. 



n 



