XVIII.] NERVE-GANGLIA, NERVE-CELLS, ETC. 2IQ 



Squeeze a little of the red pulp between two cover-glasses, and 

 treat it as recommended for the methylene-blue preparation. It 

 would bo difficult to get preparations that surpass in beauty those 

 prepared by the methylene-blue method of Thanhoffer. 



(iii.) Make a cover-glass preparation from a fresh spinal cord. 

 Heat one of them by passing it two or three times through the flame 

 of a Bunsen-burner. Thereby the proteids are coagulated and 

 partially charred. In some of these preparations good views of the 

 blood-vessels may also be obtained. 



(a.) Observe especially in the methylene-blue preparation the 

 large cells with numerous branched processes ; some of them are 

 very long, and each shows distinct fibrillation. 



(/>. ) The unbranched axis-cylinder process. 



(e.) The body of the cell, nucleated and nucleolated, with its cell- 

 contents, traversed by blue-stained fibrils, running in certain definite 

 directions through the cell. 



Other forms of nerve-cells are referred to under Cerebrum and 

 Cerebellum. 



ADDITIONAL EXERCISES. 



11. Motor Nerves to Muscles. (i.) If the skin over the sternum of a small 

 frog be divided longitudinally, on raising the skin a small thin muscle 

 musculus cutaneus pectoris will be seen running from the skin to the sternum. 

 Keep the muscle stretched and " fix " it by pouring on it a little osmic acid. 

 Cut out the muscle, and after dehydrating, mount it in balsam. It is apt to 

 darken on exposure to light. 



( L) Observe the nerve is black sending branches over the muscular fibres ; 

 trace these onwards over the muscular fibres until a single nerve-fibre is found. 



(H) Note that when a nerve-fibre divides, it does so always at a node of 

 Ranvier. The nerve-fibre can be traced to a muscular fibre, but it apparently 

 stops abruptly, because the myelin stops where the nerve pierces the sarco- 

 lemma. Other methods are required to see the termination within the sarco- 

 lemma. 



(ii.) May's Method. Select a thin muscle, e.g., the cutaneus pectoris, 

 sartorius, mylo-hyoid, &c., and place it in water containing 2 per cent, glacial 

 acetic acid for twelve hours. Make fresh the following mixture : 



| per cent, potassio-gold chloride . . . I cc. 

 2 ,, osmic acid . . . . . I ,, 



2 ,, glacial acetic acid . . . 50 ,, 



and place the muscles in it for 2-3 hours. Then transfer them to the following 



mixture : 



Glycerine . . . . . . . 40 cc. 



Water 20 ,, 



Hydrochloric acid (25 per cent.) . . . . I ,, 



for several hours. They become very transparent, and can be investigated in 

 glycerine or Farrant's solution. 



