THE SYSTEMS CONCEPT 7 



within the containing walls of the living thing: the biological system, or the 

 living system. It was in the military campaign of ancient times that the idea 

 or concept of control, within the military system, began to creep in. In mod- 

 ern military systems, in educational, government, and business systems, the 

 idea of organization and control by the central authority of the system has 

 been developed. The concept has reached its highest state of definition and 

 description in military defense systems — based principally on the extension 

 of the use of electronic circuitry to other tasks than those performed by the 

 simple oscillators of thirty years ago. Nevertheless, in those days a one-tube 

 affair had all the elements of a modern system : a detector or source of in- 

 formation fed a voltage signal into the grid of the vacuum tube; the signal 

 modified the plate current by exercising a control over the direction of flow 

 of electrons in the tube; the modified plate current passed through an ex- 

 ternal load of resistors, the voltage drop across one of which was fed back 

 into the input grid and exerted instantaneous control of the plate current; 

 while the voltage drop across the rest of the load was used to perform the 

 task assigned — in this case to feed the stable oscillating voltage into further 

 circuitry. 



The elements of this system are simple enough: a detector or source of in- 

 formation (grid input), the transmission to a central authority (the grid), the 

 control by the authority of expenditure of energy (in the plate circuit), and feed- 

 back of part of the expended energy into the central authority so that the 

 latter can know whether or not the energy is being expended in the desired 

 manner and make corrections if necessary. One other element which the 

 simple tube circuit does not have is the facility of being able to store informa- 

 tion for use when required. A modern computer has this facility. 



The living thing, and man especially, if a self-contained system (Figure 1-1) 

 in this sense, having all the essential elements, with versatility and adaptability 

 as well. The sensory organs (which enable one to see, touch, taste, smell, 

 and hear) are the detectors of relevant information. Nerve is the transmis- 

 sion line to the central authority, the brain, which stores information, ana- 

 lyzes and abstracts the relevant part, decides what to do, and then dis- 

 patches the necessary commands (electrochemical signals) to the nerve for 

 transmission to the muscles (say) which expend energy in response to the 

 command. Both a part of the muscle's expenditure and a continuous ob- 

 servation by the sensory organs feed back information to the brain so that 

 the central authority can know if the commands are being carried out. If 

 not, corrective commands can be dispatched. 



Each of the ten chapters to follow is concerned with some aspect of man's 

 operation as a system. He is the most complex system we know, to be sure, 

 and it is not always immediately obvious what is the relation between the 

 detail which we must describe and the over-all systems concept. However, 



