4 LECTURE I. 



turbance in the metabolism of the cell. At present we are very far from 

 gaining insight into the physiological processes concerned in cell-metab- 

 olism, and still less should we expect to obtain already a clear picture of 

 pathological disturbances. This opens up for us a particularly enticing 

 field for further investigation, the foundations of which must rest upon 

 physiological chemistry. It is apparent from this cursory glance that the 

 tasks of physiological chemistry are extremely varied. 



In order to be able to form a correct judgment of results brought for- 

 ward in a field of investigation, it is necessary to decide in the first place 

 whether the methods employed are satisfactory and rest upon a firm 

 basis. The methods used by the physiological chemist are for the most 

 part those of pure chemistry. Such experience forms the basis of his 

 work. We shall soon see that in spite of the fact that in many cases 

 perfectly similar methods are employed, there is a marked difference in the 

 two fields of investigation. Chemistry, we know, is an exact science. 

 This designation means, more than anything else, that the chemist arrives 

 at his conclusion by carrying out from case to case a direct proof, in a 

 perfectly objective manner. If he discovers a new substance, he is able 

 by various processes to so purify it that by its crystalline appearance, the 

 results of analysis, its melting-point, molecular weight, etc., and by a study 

 of the substances he can form from it, he can decide whether it is a simple 

 substance or a mixture. Finally, he can decompose the substance, it may 

 be by hydrolysis, or perhaps by oxidation, or by reduction, thus transform- 

 ing it into constituents of known composition, or into some other well- 

 known compound, and in this way eventually establish its composition in 

 all its details. But even after all this work the chemist is not satisfied. 

 He is not absolutely positive that he has a substance of definite constitu- 

 tion until he has succeeded in effecting its synthesis. To be sure, meta- 

 physical speculations also play an important part in the domain of pure 

 chemistry, and rightly. This has long since been shown to be justifiable 

 on account of the fruitfulness of such speculations. The chemist must 

 never forget, however, where the facts end and where the hypothesis 

 begins. 



Let us see now how the physiological chemist conducts his proofs. One 

 might be tempted to believe that an insight into the chemical processes 

 which take place in the organism would be obtained soonest if we chose for 

 our study the simplest form of organized being, the single cell, i.e., a unicell- 

 ular individual. A little thought, however, shows us that the morphological 

 unity of the cell corresponds to an uncommonly complicated cell-mechan- 

 ism. Each cell-unit here takes up nutriment, decomposes and assimilates 

 it, and eventually breaks it down to deposit at last the final products of 

 metabolism. All of these processes take place in a single minute cell. 

 From this point of view, every morphological differentiation must in a 



