be interesting to see whether it occurs in the cell which 

 has been deprived of its nucleus, in order to thrw light 

 upon the supposed synthetic function of the nucleus. 

 This point is taken up later. 



Having failed to obtain growth with simple compounds 

 of nitrogen, the organisms were nov/ supplied with amino- 

 acids. The use of single amino-acids was not promising, 

 oome reproduction v.-as obtained with a saturated solution 

 of tyrosine, but the animals soon died. A mixture of 

 amino-acids was then prepared in the following way: 



Five grams of Hammarsten's casein was heated for 

 twenty hours with 100 cc of a molecular solution of sulph- 

 uric acid. The hydrolysis was perfor^.ed on a water bath 

 in a flask fitted with a reflux condenser. At- the hydrol- 

 ysis, when the solution no longer gave the biuret reaction, 

 a saturated solution of barium hydroxide was added until the 

 reaction v/as slightly alkaline, and the solution boiled to 

 remove ammonia. Dilute sulphuric acid was added until very 

 slightly acid, and the solution filtered hot. The barium 

 sulphate precipitate, which had adsorbed much of the humus 

 substance, was not washed. The solution was exactly neutral- 

 ized with s'odium hydroxide, and the resulting solution, 

 whose volume v/as 700 cc, had the following properties: 



(58) 



