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 n 23 n 

 Nitrogen n 15 n 

 Hydrogen m 7 n 

 Sulphur M 2 II 



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 foods., 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. Movement. — Living protoplasm exhibits the power 

 to move, owing to its contractility. A drop of oil moves 

 according to the forces of gravity and capillarity, buf 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 irritable . ox 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. 



