VITAL FUNCTIONS OF PROTOPLASM. 7 
colour with copper sulphate and sodium hydrate, and a pink precipi- 
tate on boiling with Millon’s reagent). They are divided into groups 
according to their degrees of solubility. Common proteids are al- 
bumens, albuminoids, and peptones. “The essential constituents of 
proteids are the elements carbon, oxygen, nitrogen, hydrogen and 
sulphur, the average percentage composition of albumen being— 
Carbon about 53 per cent. 
Oxygen mo 23 " 
Nitrogen 1 15 u 
Hydrogen u 7 " 
Sulphur 4 2 " 
Thus the physical and chemical evidence is in favour of 
regarding living matter or protoplasm as an aggregate of 
substances of high chemical constitution and of an unstable 
nature. 
Primary Vital Functions of Protoplasm. 
1, ALIMENTATION,—Living matter has always, if in suit- 
able surroundings, the property of aggregating to itself 
foreign substances which are termed /vods, and thereby in- 
creasing in bulk. The food is by necessity of an insoluble 
or non-diffusible kind, and it has, before it is available for 
absorption into the substance of the protoplasm, to undergo 
a process of reduction to a soluble condition. This process 
is known as digestion and has, by its nature, to be conducted 
in the body of the organism. 
2. MovemMENT.—Living protoplasm exhibits the power 
to move, owing to its contractility. A drop of oil moves 
according to the forces of gravity and capillarity, but an 
organism can move in a definite direction in response to 
other stimuli. The movement is essentially the same 
throughout and consists of shortening of the organism, or 
part of the organism, in one or more directions and a 
corresponding lengthening in others. The movement 
implies a loss of kinetic energy and the setting free of 
heat. 
3. SENSATION.—Protoplasm is zrrifable or capable of 
responding to certain stimuli. The demonstration of this 
fact lies in the preceding property of movement, for outside 
our own consciousness we have no means of recognising 
the effect of a stimulus except by its result in movement. 
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