130 THE CELL 



cut in two the part which did not contain the nucleus would only 

 live for a short time, while the other part would functionate 

 normally. The nucleus is, therefore, necessary for life. Ultrami- 

 croscopic examination shows that the grey mass is a colloidal 

 (emulsoid) solution in water. Chemical analysis of dead amoeba 

 confirms the ultramicroscopic examination. Water to the extent 

 of about 75 per cent, acts as dispersion medium for a colloidal 

 complex and as a solvent for certain crystalloids. The colloid is 

 an aggregate containing protein, fat and carbohydrate. The 

 crystalloids are to some extent adsorbed on the surfaces of the 

 colloidal mass and to some extent are in free solution. The 

 elementary chemical composition conveys little information as 

 to the properties of the complex. To say that protoplasm contains 

 a certain percentage of carbon, hydrogen, oxygen, nitrogen, 

 sulphur and phosphorus in a colloidal state, and potassium, calcium, 

 sodium, chlorine and phosphorus in solution is not of much use 

 as a contribution to the study of life. It is just as preposterous 

 to appraise the value of great pictures in terms of the chemical 

 composition of the paints and pigments employed as to attach 

 any great significance to the chemical elements of a dead cell. 

 What is of great importance is the physical state of the matter, 

 just as the value of a painting lies in the physical juxtaposition 

 of pigments, an artistic blending of colour, light and shade, 

 whereby the eye is pleased, so the life of a cell depends on the size, 

 consistency, etc., of the colloid-crystalloid complex forming its 

 protoplasm. " When," says Schafer, " the chemist succeeds in 

 building up this complex it will, without doubt, be found to 

 exhibit the- phenomena which we are in the habit of associating 

 with the term ' life '." What are the phenomena commonly 

 associated with the term "life," especially as manifested by a 

 unicellular animal ? 



(a) Movement is the commonest phenomenon indicative of life. 

 Amoeba moves. It extrudes footlike processes, pseudopodia 

 (Gr. pseudio, false ( similar to), podes, foot), at one part and 

 retracts them at another and so moves along. Similar amoeboid 

 movements are characteristic of the white cells or leucocytes 

 (Gr. leukos, white) of the blood. Recently, Goodrich has carefully 

 studied these movements of the leucocytes. He produces camera 

 lucida drawings to show that the pseudopodia usually take up 

 the form of expanded motile membranous folds when the living 

 leucocytes are examined suspended freely in the normal fluid 

 which is their habitat. One of his drawings is reproduced in 



