130 LECTURE VII. 



amines, which are almost entirely built up of di-amino acids. There are 

 many intermediate stages between these two groups; thus, the histons 

 contain more di-amino acids than the above substances, which are rich 

 in mono-amino acids, although less than the protamines. The common 

 proteins, albumin, globulin, etc., occupy an intermediate position between 

 the silk, elastin, etc., group and the histons. In this way we may classify 

 the proteins as follows: 



1. Proteins with less than 10 per cent of di-amino acids elastin, 

 silk, etc. 



2. Proteins with about 10 to 15 per cent of di-amino acids serum- 

 albumin, serum-globulin, casein, etc. 



3. Proteins with from, say, 20 to 30 per cent of di-amino acids histon 

 from the thymus. 



4. Proteins with larger amounts of di-amino acids (sometimes 80 per 

 cent or more) (protamines: salmine, clupein, etc.). 



Our present knowledge is too inadequate for us to classify all proteins in 

 this way. The boundaries of the different groups are not sharply defined, 

 and we observe all sorts of intermediate stages between them. Further- 

 more, there is no doubt but that a member of one group may be trans- 

 formed while in the tissues so that it belongs to a different group. F. 

 Miescher J has called our attention to an interesting example of such a 

 transformation. It is well known that, as the spawning season approaches, 

 the salmon journeys from the ocean into fresh- water streams. During the 

 entire period of several months in which it remains in the fresh water, the 

 fish eats nothing. On leaving the salt water it is a powerfully muscular 

 fish. These muscles are required for the stemming of strong currents. 

 Its sexual organs testes and ovaries are immaturely developed. 

 Gradually, however, the large lateral-dorsal muscle becomes smaller, 

 while the sexual organs assume large dimensions. There can be no 

 doubt but that the latter develop at the expense of muscular tissue. The 

 mature testis contains a protein rich in di-amino acids, known as salmine. 

 There is but little of this substance present in the immature organ. It 

 then consists chiefly of a histon-like substance. Histons, as a rule, do not 

 occur in any considerable amount in the muscles. It is very probable 

 that the protein in the muscles of the salmon loses di-amino acids, thus 

 increasing the proportion of di-amino acids in the protein, eventually 

 producing protamine with the intermediate formation of a histon. It is 

 highly interesting for the development of our knowledge concerning the 

 metabolism of proteins that we should study such relations further. 



There is no question but that we shall shortly be able to classify the 

 proteins according to chemical principles. We must determine in the 



1 Die histochemischen und physiologischen Arbeiten von Friedrich Miescher. 



