12 GERM-CELL CYCLE IN ANIMALS 
a hextose (carbohydrate) ; and 
phosphoric acid. 
Its formula, according to Schmiedeberg, is CoHs6 
NywOi,.2 P:O;, and according to Steudel, CusHs7 
N,;0...2 P:O;. Considerable progress has been 
made, especially by Emil Fischer and his students, 
in the synthesis of protein-like bodies. Many com- 
plex polypeptides have been built up which resemble 
peptones in many of their reactions and when in- 
jected into living organisms appear to be utilized 
in metabolism in much the same way as are native 
proteins. 
We are still, however, very far from an adequate 
understanding of the nature of chromatin. Della 
Valle (1912), for example, after an exhaustive study 
of the physico-chemical properties of chromatin 
both in the resting nucleus and in the dividing cell, 
has concluded that this substance resembles that 
of fluid crystals. ‘‘Consequently all of the pheno- 
mena presented by the chromosomes; their mode of 
origin, differences in size, state of aggregation, form, 
structure, colorability, optical characteristics, varia- 
tions in form, longitudinal division and the phenom- 
ena which follow this mode of scattering, demon- 
strate that the chromosomes are crystalloids.” 
Two other primary constituents of protoplasm may 
be mentioned briefly. The phosphatide, lecithin, 
belongs with cholesterin to a group of compounds 
called lipoids. It consists of glycerophosphoric acid 
plus certain fatty acid radicles, such as stearic acid, 
oleic acid, etc., and a nitrogenous base (cholin). It 
