12 LECTURE I. 



The latter alone cause the science to progress, upon a solid foundation. 

 They assure an objective investigation, and above all else one that is 

 free from prejudgment. Certainly hypotheses and speculations are of great 

 value, and their importance should not be underestimated. They form 

 the framework upon which we can build further. The facts, however, 

 should never be adjusted in accordance with them. The facts, and never 

 the hypotheses must always be decisive. This warning is not unnecessary, 

 for in contrast to the exact sciences such as chemistry and physics, 

 here in physiological-chemical investigation the hypotheses step boldly 

 into the foreground, especially in questions concerning metabolism, and 

 in particular that of the cell substance. 



We make these few preliminary remarks in order to show at the start 

 the nature of our lectures and the principles which are authoritative. It 

 will be our aim to define as sharply as possible what discoveries are to be 

 regarded as well-established facts and at what place the probability 

 proofs are justifiable. Above all else we shall strive to follow every 

 separate food-stuff from its introduction into the organism to its complete 

 breaking down and the elimination of the end-products in order thus to 

 obtain a comprehensive view of its behavior in the organism and 

 its participation in metabolism. We shall intentionally consider the 

 building materials and composition of the separate organs only in 

 special cases. This knowledge we acquire in studying metabolism. 

 A consideration of the quantitative relations in which the different sub- 

 stances are present would be of use to us only when the separate values 

 are based upon a broad foundation and upon a great many observations. 

 For the present our methods are not adequate to give us a satisfactory 

 picture of the building up of the separate tissnes. Neither is our 

 knowledge sufficient to permit the valuation of the results for compara- 

 tive studies, nor are we in general in a position to draw conclusions 

 with regard to the functions of certain organs from a knowledge of 

 their composition. In the special cases where this is possible we shall 

 speak of it. 



