CHEMISTRY OF THE CELL NUCLEUS 201 



more fully in later pages, if I state at this point that the 

 stainable substance is a kind of protein or albuminous 

 material. Chemists at the present day divide the proteins into 

 two main groups, each of which has many subdivisions. The 

 first of the two main classes is designated that of the simple 

 proteins. The word " simple " is somewhat of a misnomer, for 

 anything in connection with a protein is so complex that 

 hitherto proteins have baffled all attempts at artificial synthesis. 

 But at any rate such proteins as are included in this class 

 (albumin, gluten, casein, gelatin, etc.) are simple as compared 

 with those in the second group, which are called the compound 

 or conjugated proteins. In these the protein molecule is 

 united to another group, also of a complex nature. Haemo- 

 globin is an instance of a conjugated protein, where the protein 

 proper is united to an iron-containing radicle termed haematin. 

 The nucleus of cells consists of or contains large quantities 

 of another conjugated protein, which has been called nuclein 

 by chemists, and there is no doubt that nuclein is identical 

 with the chromatin or chromoplasm of the histologist. Nuclein 

 is a compound of protein with an organic acid rich in 

 phosphorus, which is named nucleic acid. In the nucleus 

 itself the protein component of the compound is small in 

 quantity, and in the nucleus which we term the head of a 

 spermatozoon, it is stated to be entirely composed of nucleic 

 acid without protein admixture ; this may be so in mammals, 

 but in fishes there is a combination in the nucleus of the 

 spermatozoon between nucleic acid and a simple kind of 

 protein termed protamine. 



There seems in fact to be a whole chain of nucleins 

 containing a diminishing quantity of nucleic acid and an 

 increasing quantity of protein ; and those which contain the 

 smaller amounts of nucleic acid are spoken of usually as 

 nucleo-proteins. Most nuclei contain so much nucleic acid 

 that they yield on analysis 10 to 12 per cent, of phosphorus; 

 whereas in the nucleo-proteins of cell protoplasm the phosphorus 

 percentage is in the neighbourhood of 2 or 1 per cent, or 

 even less. 



These facts and others to be described later have been 

 made out by two sets of methods, those of micro-chemistry 

 and those of macro-chemistry. In the former the reagents 

 are applied to the microscopic object, and the change, colour 



