40 LIFE: ITS ORIGIN AND NATURE 
we become tired and exhausted, and this exhaus¬ 
tion can only be relieved by rest and sleep—and 
not by adding more fuel, in the shape of food. 
Sleep, therefore, is u very peculiar condition, 
which differentiates the human body from any 
form of steam-engine known to us. It seems 
to show us that there is a great difference be¬ 
tween the method by which the human body 
replenishes its energy, and the ordinary chem¬ 
ical combustion theory, which is applicable to 
the steam engine. 
(2) Many persons, who have become weak¬ 
ened by the onset of some disease, will find that 
their energy is increased, by abstaining from 
food altogether, for a longer or shorter period— 
that is, by fasting. I have seen many cases in 
which the patient was so weak that he was 
hardly able to walk upstairs. Yet, after having 
abstained from all solid food for a number of 
days, he was enabled to walk several miles 
daily, and felt better and stronger than he had 
for years past! This is readily understood by 
students of therapeutic fasting, but, without 
going into the details now, it may be pointed 
out that such an increase of energy could hardly 
be expected, if the source of our bodily energy 
were the food we eat! 
Other arguments might be advanced in sup¬ 
port of this theory, but enough has been said, 
perhaps, to indicate that it is a legitimate in¬ 
terpretation of the observed facts, and that it 
is in accord with the findings of physiological 
science. 
Professor Hans Driesch has advanced other 
views in favor of the vitalistic interpretation, 
