I.] THE FROG. 135 



Examine the thinnest pieces under your highest 

 power. 



a. The fibre is seen to be marked out into a 

 close-set series of alternately light and dark 

 transverse strice^ the former being in all pro- 

 bability the narrower. 



^. Keep your eye steadily fixed on a given piece 

 while you alter the focus — parts which were 

 originally dark now become light and vice 

 versa. 



y. Examine a fragment in which the cross stride 

 are very distinct, still more minutely. When 

 in exact focus the following will be seen. 



The septal zones ; obvious as the afore- 

 named clear strise. 



The ititerseptal zones ; alternating with and 

 of greater thickness than a. Each is longi- 

 tudinally striated. 



The septal lines ; dark lines of great deli- 

 cacy, one in the middle of each septal zone; 

 seen, on close examination, to appear as a 

 parallel series of minute dots. 



Very generally the fibre is constricted at each 

 septal line, having thus a beaded appearance. 



8. Repeat the operation described at /?. and note 

 the different optical eftects which are pro- 

 duced at different levels of focus. 



V. Alelland's method. Place some fragments of 

 fresh muscle in i per cent, acetic acid solu. for 

 10 seconds ; transfer to i per cent, gold chloride 

 solu. for I hour and then to 25 per cent, formic 

 acid solu. for 48 hours or longer (to be kept in 



