I06 STRONG. [Vol. X. 



Equal volumes of i^ solution of each avoided this, and also 

 gave some good results. Zinc sulphate seems to act similarly 

 to the sodium salt and can be mixed with the silver in larger 

 proportions without producing a precipitate. 



It must not be understood that this latter modification gives 

 ideal results. In some cases it seems to be an improvement, 

 but further experience is necessary to ascertain its precise 

 value. In the tadpole it has yielded especially good prepara- 

 tions of the nerve terminations in the heart (PI. IX, Fig. 14). 

 The specimens should be placed in pure silver nitrate a while 

 previous to placing them in alcohol, in order to wash out the 

 sulphate, otherwise the alcohol will precipitate the latter in 

 the tissues. The specimens are left in the dark while in the 

 osmium-bichromate and in the silver bath. 



Preservation. — If, for any reason, specimens cannot be cut 

 and mounted immediately after impregnation, they can be best 

 preserved in the silver bath. Specimens will often keep thus 

 for months, but there is considerable risk of deterioration. 

 This latter is probably due, as von Lenhossek suggests (37), 

 to a slow precipitation of the silver in solution, .so that in time 

 the specimen is left simply in water which, in turn, bleaches 

 out the stain. Another cause of deterioration appears to be 

 a gradual darkening of the whole tissue. It is obvious from 

 this that if it is necessary to keep the specimens some time 

 before cutting, two precautions should be taken, {ci) the speci- 

 men should be kept in a liberal supply of the silver solution 

 of full strength, and {b) it should be kept strictly in the dark 

 in order to prevent, as far as possible, a gradual secondary 

 reduction of the silver. 



The double and triple impregnation, as recommended by 

 Cajal (13), was tried with good results. The exact details of 

 procedure in technique are placed in an appendix. 



II. Detailed Description of the Nerves and their 



Components. 



The most direct treatment seemed to be, first, to examine 

 each nerve in detail, with a view to ascertaining its com- 

 ponents, each section concluding with a table summarizing the 



