28 



PHYSIOLOGY 



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, protamine. 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 com- 



JlJi 



D 



FIG. 8. Nucleated and non-nucleated fragments of Amoeba. (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 con- 

 tractile vacuole. 



bined 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. 



In order to appreciate the part played by the nucleus in the ordinary 

 cell processes, we must study the behaviour of cells or parts of cells deprived 

 of a nucleus and compare it with that of similar cells or parts of cells still 

 containing a nucleus. By means of a fine needle it is possible to divide the 

 larger protozoa into two pieces, one with and one without a nucleus. Hofer, 

 experimenting on the amoeba, found that the fragment containing the nucleus 

 quickly regenerated the missing part and pursued a normal existence. On 

 the other hand, the non- nucleated fragments showed no signs of regeneration. 

 They might, indeed, live as long as fourteen days after the operation (Fig. 8). 



