The addition of various salts was tried, but no improve- 

 ment was observed. Cystine and tryptophane, so i^nport- 

 ant in the nutrition of highei- animals, were added to 

 the solution in concentrations which were shov/n not to 

 be toxic. A small amount of milk was added to provide the 

 unknown "accessory" food substances and certain salts. 



No adequate synthetic medium w.-is found for Ameba 

 proteus. The failure may be due to some peculiarity 

 of the cell, such as its enormous size, or a low 

 permeability. 



(41) 



