22 PRINCIPLES OF BIOCHEMISTRY 



which occur in living matter. The life of any one cell consists in a 

 multiplicity of parallel reactions, interrelated, interdependent, and 

 interwoven into a bewildering complex. Multicellular organisms, such 

 as ourselves, consist of millions of such cells. When the reader is 

 reminded that the reactions in each organ or group of cells and possibly, 

 even in each individual cell, possess an individual character of their own, 

 and that these reactions are excessively sensitive to external agencies, 

 the complexity of the task of unravelling the separate reactions and 

 tracing their individual progress must be evident. 



It follows from the complexity of the phenomena that the regularities 

 and relations observed by the biochemist are rarely capable of formula- 

 tion with such precision as those which are observed by the physicist 

 or chemist. To illustrate this fact, let us consider the difficulties 

 attendant upon the investigation of one of our simplest problems, 

 to wit, that of the mode of action of the protein-digesting ferment 

 Trypsin. We have first of all to overcome the difficulty of obtaining 

 pure protein. That obtained (and a "pure" protein in the sense that 

 inorganic reagents may be "pure" has never been prepared), we then 

 have the difficulty of obtaining a pure trypsin, a difficulty which has 

 never been even partially overcome. In fact we certainly possess no 

 pure trypsin and we have, moreover, no method of ascertaining how 

 impure our preparations are. Not only are our preparations of trypsin 

 impure, but they frequently contain several ferments which digest 

 proteins, a fact which has only recently come to be appreciated. 

 Notwithstanding all these obstacles we have found that if trypsin 

 be allowed to act upon protein, with certain necessary precautions, a 

 regularity may be observed in the rate of decomposition of the protein 

 by the ferment, and this regularity may even be formulated in mathe- 

 matical terms. We are not surprised to find, however, that the agree- 

 ment between the formula and the experimental measurements (of 

 quantity of protein digested) is not extremely exact. Under very 

 favorable conditions the requirements of theory and the findings of the 

 investigator may agree to within one per cent, of their mean value. 

 In a purely chemical problem an agreement to within one-tenth of a 

 per cent, is anticipated and not infrequently obtained. In physics 

 or in astronomy an agreement to within one one-hundredth of a per 

 cent, is not in the least exceptional. As the uncontrollable adventitious 

 variables become fewer, it will be observed, the agreement between 

 formulae and experimental data becomes more and more precise. 



Hypotheses of a more general character, not admitting of mathe- 

 matical formulation, share in this disadvantage, and hence it arises 

 that a larger proportion of hypotheses in biological sciences are of 

 uncertain or very questionable validity than of those in the so-called 

 "exact" sciences. But the difference is merely a matter of degree 

 and tends progressively to diminish. All scientific hypotheses and 

 "laws" are subject to a marginal inexactitude, and all human precision 

 is relative. As our acquaintance with any field of investigation grows 



