30 



PHYSIOLOGY 



simple proteins, but built up with other complex bodies to form con- 

 jugated proteins. Whereas in the cytoplasm these conjugated proteins 

 consist chiefly of compounds of protein and lecithin, in the nucleus 

 the chief constituents belong to the class of nucleo-proteins. The 

 nucleo-proteins are of varying composition, and are distinguished 



B 



FIG. 8. Nucleated and non-nucleated fragments of Amaha. (WILSON after HOFER.) 

 A, B. An Amoeba divided into nucleated and non-nucleated halves, five minutes 

 after the operation. C, D. The two halves after eight days, each containing a 

 contractile vacuole. 



chiefly by the large amount of phosphorus in their molecule. A nucleo- 

 protein can be broken down into nuclein and protein. Nuclein can 

 be broken down into nucleic acid and a protein-like substance, prota- 

 mine. Nuclei differ among each other and at different periods of their 

 existence or in different conditions of activity according to the greater 

 or less amount of protein which is combined with the nuclein. The 

 latter seems to be the essential constituent of cell nuclei and to be 

 present in only small quantities in the cytoplasm. The properties 

 and reactions of these bodies will be dealt with at greater length in the 

 next chapter. 



