i8 THE ACTIVE FORCES OF LIVING ORGANISMS 



only loses about an eleventh part of its weight.* But, 

 on the other hand, birds possess nucleated corpuscles, 

 and yet they of all animals are the first to suffer from 

 want of food, whilst their respiration is of a very 

 intense nature. One day's total abstinence, it is 

 affirmed, will kill a sparrow, three days a thrush, 

 the respiratory intensity, as measured by the relative 

 quantities of oxygen absorbed and carbonic acid and 

 nitrogen exhaled, being seven times greater in birds 

 than in mammifers, whilst that of the latter is ten 

 times that of reptiles. It does not, therefore, seem 

 to be possible to establish any connection between the 

 presence of the nucleus and the rate of activity of the 

 vital processes. On the other hand, however, there 

 seem to be some reasons for supposing the develop- 

 ment of the nucleus to be inversely proportional to 

 that of the nervous system. The nucleus is by 

 common consent a centre of vitality for the cell. If 

 we estimate the vitality of the tissues in the lower 

 animals by the readiness with which portions separated 

 from the organism reunite with it — as, for instance, 

 in the case of an earthworm, or by the long-continued 

 twitchings to be observed in a spider's legs when cut 

 off from the body — we shall be inclined to conclude 

 that life in these and similar types is less centralized 

 than is the case with mammifers in general. A 

 parallel to these conditions may be found in institu- 

 tions of human origin ; for as the central authority in 

 any country increases, the power of the individual as 

 * Letoumeau, ' Biology ' (trans.), p. 147. 



