42 
IOWA ACADEMY OF SCIENCES. 
It is worthy of special emphasis that the chemical reac- 
tions of the cell invariably occur in a liquid which is 
really a dilute solution of electrolytes. Free ions certainly 
have to be reckoned with in the phenomena of cell-life. 
Among the organic constituents of the animal cell, the 
proteids must be accorded first place. These exist in sev- 
eral degrees of complexity. The simple globulins and 
albumins are found in both cytoplasm and nucleus; these 
represent the lowest step in the process of assimilation. 
Combined proteids hold a larger place in cell-life, particu- 
larly the members of the nuclein series. Chromatin is a 
nuclein rich in nucleic acid, relatively poor in proteid. Its 
richness in acid is expressed by the deep stain which it 
assumes with basic dyes. The nucleolus has a lower per- 
centage of nucleic acid, a higher percentage of proteid. 
Nucleo-proteids are characteristic of the cytoplasm, a max- 
imum of proteid having combined with the nucleic acid. 
It is highly suggestive that the successive additions of pro- 
teid to the molecular constitution of the nucleo-proteids 
of the cell take place from the chromatin outward into 
the cytoplasm. 
Lecithin and cholesterin are components of both 
cytoplasm and nucleus. The place of lecithin may be 
next to that of the proteids in order of importance. Its 
presence in quantity in nervous tissue is the basis for the 
ready absorption and specific action of anesthetics. 
The carbohydrates and fats of the animal cell are 
marked off sharply from the foregoing classes of constit- 
uents by the fact that they are limited to inclusions in 
the cytoplasm. 
A proper interpretation of the conditions for cell-life 
requires us to hark back to the fundamental work of 
Graham on colloids. Because of the high percentage of 
proteids in the cell, the bulk of protoplasm consists of 
colloidal matter in water. Following the nomenclature of 
Graham, protoplasm is a sol; and since the colloidal 
particles are held suspended in water, protoplasm is really 
a hydrosol. Protoplasm exhibits the properties of colloidal 
solutions generally, passing readily into the gel condition, 
