276 LECTURE XIII. 



apparently combined with albumin. Nucleoproteids have, however, been 

 obtained by salting them out. Although we have no doubt that such 

 compounds with nucleic acid exist, especially of the basic proteins, like 

 the histones and protamines, still we must admit that no convincing proof 

 has yet been presented that there is such a state of combination in the cells 

 themselves. We are accustomed to look upon substances which we always 

 find in given localities, and are never absent, as being particularly important 

 for the functions of the cells and tissues, especially when we find these in 

 the parts of cells to which we assign great importance. Although such an 

 assumption is probably true, we should be concealing the actual state of 

 our knowledge, if we failed to mention the fact that the exact significance 

 of the nucleoproteids is still unknown to us, and that we do not, at present, 

 understand their relations in cell-metabolism. 



We have already stated that the nucleoproteids are composed of two 

 constituents, one of which is an albumin, and the other nucleic acid. It 

 is not yet clear to us how we shall conceive the formation of the proteids 

 from these two components. It has been shown that the decomposition 

 into albumin and nucleic acid portions does not always take place as if it 

 were a simple process. We obtain the impression that the nucleic acid is 

 united with two parts of albumin. One part can be easily split off, the 

 other with much more difficulty. The following scheme expresses this 

 conception: 



Nucleoproteids 



7\ 



Albumin Nuclein 

 /\ 



Albumin Nucleic acid. 



When albumin is split off from the nucleoproteid, a part of the protein 

 remains combined with the nucleic acid. This product is called nuclein. 

 This was first observed by Miescher on digesting a nucleoproteid with 

 pepsin and hydrochloric acid. The albuminous portion, which is most 

 easily split off, is decomposed, while the nuclein precipitates. More recent 

 investigations have shown that active pepsin may even disintegrate the 

 nuclein, thus leaving the pure nucleic acids behind. 



We are especially interested here in the nucleic acids. We have already 

 considered the protein constituent a v s far as it is known. All the nucleic 

 acids contain phosphorus. When decomposed, they produce phosphoric 

 acid and nuclein bases. Other products are also formed when the nucleic 

 acids are decomposed. A carbohydrate group has been split off in some 

 cases, while from others pyrimidine groups have been obtained. We shall 

 here first consider all of the known cleavage-products of the different 

 nucleic acids, and not pay any attention at present to the composition of 

 these different acids. All of these nucleic acids which have been studied. 



