4O DEFENSIVE FERMENTS OF THE ANIMAL ORGANISM 



nature. The cause the primurv process escapes 

 our notice, partly because at the time we do not know 

 how best to state the problem, partly because we have 

 no methods at our disposal for an experimental 

 investigation of the case. 



In all biological problems it is remarkable how 

 entirely dependent we are upon the philosophy and 

 the methods employed in the exact natural sciences. 

 \Ye transfer all that is there obtainable to the 

 problems of biology. For some years certain ideas 

 prevail, only to recede as soon as a new impulse or 

 a new success in the domain of physics and chemistry 

 directs a host of workers into new paths. -We drill 

 and work until a new gallery is driven into the rock 

 of puzzles which is found in every cell. Very often 

 the gallery ends blindly, but on its way has given 

 rise to numerous interesting discoveries. Sometimes, 

 however, the pioneer work is crowned with success. 

 An important stage is left behind, and a new outlook 

 gained. The final aim, however a complete in- 

 sight into the metabolism of the cell still lies far 

 ahead. Yet the knowledge we have acquired serves 

 as a compass to keep us on the right road. The 

 careful traveller will never leave anything unnoticed, 

 for observations which often seem but trifles mav 



m> 



point the way to entirely new problems. 



In studying the functions of the cell we must never 

 forget that there is not a single substance which is of 



