detected. The shrinkage caused by the glucose would 

 render the detection of grov/th difficult even if present. 



Of special interest, however, are the three cases 

 of cell division seen in the urea solution. Altho hundreds 

 of amebas have been kept under daily observation until 

 they were completely disintegrated, no single case of 

 cell division was ever observed unless food substances 

 were supplied; and with tv/o possible exceptions, no divis- 

 ion v/as observed unless a source of nitrogen was added. 

 On the other hand, divisions have been repeatedly observed 

 in solutions containing urea or certain amino acids. That 

 the division is not simply the result of the stimulating 

 action of the urea upon the nrotoplasm is shown by the ef- 

 fect of urea solutions to which no glucose is added. In 

 such solutions, tht amebas not only do not divide, but 

 they die more quickly than in water alone. Urea in the 

 absence of glucose is simply a mild poison, but w^hen urea 

 and glucose are used together, the animals live longer, 

 have a more normal appearance, and may even reproduce. 

 The necessity of using the two substances together indicates 

 that they are built up or combined to form some more com- 

 plex substance which is of use to the organism. 



if this is a true c ise of organic synthesis, it woulci 



(57) 



