188 LECTURE IX. 



problem of the constitution of albumin! They all anticipate new impulses 

 therefrom new developments; and, above all, new methods. Although 

 many dreams will not come true and many hopes may be unfulfilled, the 

 biology of the albumins will, undoubtedly, especially in the narrower sense, 

 open new fields of effort, and, when placed upon a satisfactory foundation, 

 will show great progress. 



Let us see now what assumptions concerning decomposition of the 

 albumins by ferments can be based upon the above observations. We 

 have seen that the first cleavage-products of albumin are the peptones. 

 We can easily imagine that the albumin molecule breaks down in the 

 first place into a series of long chains of amino acids. Even these may 

 be much differentiated among themselves. It is not necessary that each 

 of these chains should contain all the amino acids present in the albumin. 

 These chains then break down into cleavage-products containing a smaller 

 number of amino acids. We can imagine hereby that a complicated 

 cleavage-product breaks down into several simpler ones, each containing 

 more than one amino acid. Many observations indicate, however, that 

 the amino acids themselves appear at an early stage. 



It is of interest that practically simultaneously with the appearance of 

 tyrosine, cystine, tryptophane, etc., in the digesting liquid, those products 

 called albumoses diminish in amount, and finally disappear. This cor- 

 responds to the observations made in the breaking down of tetrapeptides. 

 As soon as the tyrosine is removed by trypsin, the albumose character 

 disappears. Tyrosine can be detected within a few hours after the 

 beginning of digestion. Subsequent decomposition takes place with the 

 constant production of more amino acid. Smaller chains are produced from 

 the peptones with larger amounts of amino acids, until finally the greater 

 part of the amino acid chains are decomposed into their constituents. The 

 peptones are therefore to be considered as a large mixture of various kinds 

 of polypeptides. The best distinction that we can make is that only those 

 polypeptides belong to the peptone class which will give the biuret reaction. 

 Unquestionably, the term peptone will gradually disappear, and we shall 

 eventually deal only with chemical individuals. 



We shall here refer, as we now do in the synthetic chemistry of albumins, 

 to di-, tri-, tetra-, and polypeptides. The biuret reaction is only used as a 

 convenience in indicating the limit of the branching compounds to be 

 included in the peptone class. The polypeptides which give this reaction 

 gradually pass over into those which no longer do so. Between the 

 peptones of the longest chains and the simple amino acids there are con- 

 tinuous transitory stages. 



The decomposition of the proteids by means of trypsin can be illustrated 

 in the following manner: 



