26 INTRODUCTION TO CYTOLOGY 



of myxomycetes^ and the spermatozoa of fish have been most frequently 

 employed, the former because of the large mass of protoplasm readily 

 available, and the latter because they yield large amounts of nuclear 

 material in a fairly pure state. By the use of stains Unna and others 

 have been able to determine the position in the cell occupied by certain 

 organic constituents. Microchemical methods have been employed 

 to some extent in the study of the inorganic constituents, but they are in 

 need of further development. The results of Kiesel's analysis of the 

 myxomycete Reticularia lyco'perdon are as follows: 



Per Cent Per Cent 



Dry Weight Dry Weight 



Proteins 29.07 Lecithin 4.67 



Oil 17.85 Cholesterol 0.58 



Glycogen 15 . 24 Nitrogen extractives 12 



Other non-reducing soluble carbo- Nucleic acid 3 . 68 



hydrates 5 . 32 Lecithoproteins 1.2 



Reducing carbohydrates 2 . 74 Unknown 5 . 87 



Polysaccharides 1 . 78 



The protein matter of protoplasm exists in relatively complex forms. 

 "The chief mass of the protein substances of the cells does not consist of 

 proteids in the ordinary sense, but consists of more complex phosphorized 

 bodies. ..." (Hammarsten). Such "phosphorized bodies" are the 

 nucleo-proteins, which are "probably the most important constituents of 

 the cell, both in quantity and in relation to cell activity" (Wells). A long 

 series of chemical investigations^ has shown that these nucleo-proteins 

 are essentially combinations of nucleic acid with proteins. 



The nucleus, as a rule, contains little or no uncombined carbohydrate, 

 fat, or salt, but is characterized rather by the abundance of a substance 

 called "nuclein, " isolated in 1871 by Miescher, who gave it the formula 

 C22H49N9P3022. It was shown by Altmann (1889) that nuclein, like 

 other nucleo-proteins, is a combination of two substances: nucleic acid 

 and a simpler form of protein, the two existing in chemical combination 

 much like an ordinary salt. Nucleic acid, which is, in turn, a com- 

 bination of phosphoric acid with certain carbohydrates and bases, seems 

 to be very much the same in all types of protoplasm. It is well known in 

 two general forms, differing chiefly in the carbohydrate constituent of the 

 molecule; in one form this is a pentose and in the other a hexose. The 

 former is known to occur in yeast, wheat, and certain animals, 

 while the latter has been found in thymus and lymph glands, blood cor- 

 puscles, and spermatozoa. The strong afl^inity of nucleic acid for organic 

 bases is responsible for the staining reactions of the chromatic nuclear 

 substance: a fixed and stained chromosome is a salt of nucleic acid with a 



2 Reinke and Rodewald (1881) and Lepeschkin (1923) on Fuligo varians (J<Jlhalium 

 septicum); Kiesel (1925. 1927) on Reticularia and Lycogala. 



^ By Miescher, Hoppe-Seyler, Reinke, Kossel, Lilienfeld, and later workers. 



