INFLUENCE OF WORK 



497 



great towns of England, and this difference is to be attributed 

 in great measure to the fact that the ideal of maternity among 

 the Boer women is more natural, and therefore higher, than that 

 among many of the degenerate dwellers in large cities. 



Richet made an interesting series of experiments upon the 

 output of carbon dioxide of dogs of different sizes, and found, as 

 the following table will show, that it bore a very constant relation 

 to the surface of the body. 



A series of similar observations made upon birds did not show 

 this constant relation between surface and mass ; this is probably 

 explained by the great difficulty of maintaining comparable condi- 

 tions as regards muscular activity. 



Influence of Muscular Work upon the Respiratory Exchange. 

 The muscles are the most important seat of respiratory exchange, 

 for they make up nearly 40 per cent, of the weight of the body 

 and are subject to great activity ; even during a condition of 

 apparent rest they are in a condition of tone, and the respiratory 

 muscles and the heart are subject to frequent contraction, alter- 

 nating with relaxation, throughout life. The practical importance 

 of the great effect of muscular exercise upon the processes of 

 oxidation in the body cannot be overestimated in these days, 

 when over-civilisation tends to weaken the physique and moral 

 fibre of man. There is no other condition, whether it be physio- 

 logical or pathological, which will produce such a great increase 



2i 



