474 LAWS OP MULTIPLICATION. 



plete, a bitch bears at a birth fewer puppies than when she 

 becomes full-grown. An accompanying allegation is, that 

 her declining vigour is shown by a decrease in the number of 

 puppies contained in a litter, " ending in one or two." And 

 then it is further alleged that, " as regards the amount of 

 work a dog has to perform, so will the decline be rapid or 

 gradual ; and hence, if a bitch is worked hard year after year, 

 she will fail rapidly, and the diminution of her puppies will 

 be accordingly; but if worked moderately and well kept, she 

 will fail gradually, and the diminution will be less rapid." 



In this place, more fitly than elsewhere, may be added a 

 fact of like implication, though of a different order. Of 

 course whether excessive expenditure be in the continual re- 

 pairs of nervo-muscular tissues or in replacing other tissues, 

 the reactive effects, if not quite the same, will be similar 

 there will be a decrease of the surplus available for genesis. 

 If, then, in any animals there from time to time occur unusual 

 outlays for self-maintenance, we may expect the periods of 

 such outlays to be periods of diminished or arrested repro- 

 duction. That they are so the moulting of birds shows us. 

 When hens begin to moult they cease to lay. While they 

 are expending so much in producing new clothing, they have 

 nothing to expend for producing eggs. 



