104 The American Naturalist. [February, 
ences in reaction. We must have more definite chemical 
knowledge before we can hope to attain to a clearer under- 
standing of the actual make up of cell protoplasm. Further, 
such knowledge is not to be obtained solely by micro-chemical 
study. The latter is surely important, but macroscopical 
methods must be relied upon mainly to furnish the desired 
information, and when we have full knowledge of the chemical 
nature of the substances present in the protoplasm, we may 
hope to find micro-chemical methods adapted to their accurate 
detection. 
What now is the state of our knowledge regarding the 
primary constituents of cell protoplasm? Taking the results 
which have been elaborated by painstaking work during the 
last ten years, I think we are justified in asserting that the 
primary constituents of the cytoplasm are especially a peculiar 
group of proteid or albuminous bodies known as nucleo- 
albumins and characterized by containing phosphorus. These 
are by far the most numerous of the substances present in the 
cytoplasm. Next in importance are simple proteids belonging 
mainly to the group of globulins, a class of albuminous bodies 
insoluble in water but readily dissolved by 5-10 per cent. salt 
solution. Lecithin comes next, a complex phosphorized body 
having a constitution similar to that of a fat and yielding by 
decomposition higher fatty acids, glycero-phosphoric acid 
cholin. This body is also insoluble in water and likewise 12 
salt solution, but is readily dissolved by ether and somewhat 
by alcohol. Another substance almost invariably present ? 
cytoplasm is cholesterin, a solid crystalline alcohol of som 
what uncertain constitution, insoluble in water and salt 
solution, but readily soluble in alcohol and ether. There — 
maining constituents of the cytoplasm are the inorgamlé 
elements calcium, magnesium, potassium and sodium unl 
with chlorine and phosphoric acid to form chlorides and 
phosphates respectively. It may be somewhat questionable 
whether all of these latter salts are primary constituents of : 
cytoplasm, although it seems quite certain that potassium 
— is present in fairly large quantities in animal cells 18 ee 
true primary constituent. Potassium phosphate is certainly 
