PHYSOSTIGMINE 



food. This, after undergoing a pre- 

 liminary process of digestion, fur- 

 nishes the raw material which the 

 living animal transmutes into liv- 

 ing protoplasm, or can utilise as a 

 source of the energy expended in 

 the course of its activities. The 

 processes involved in the building 

 up of food into protoplasm and the 

 breaking down of protoplasm into 

 waste-products are included under 

 the term Metabolism, which forms 

 an important section of physiology, 

 and the study of metabolism shows 

 that not only food, but also a sup- 

 ply of oxygen, is necessary for the 

 life of the organism. 



In the lowest forms of animal 

 life all the processes just described 

 take place within the compass of a 

 single cell. But the study of ani- 

 mals higher in the scale of evolu- 

 tion at once reveals differentiation 

 of both structure and function, 

 since these animals consist of many 

 cells, which have become modified 

 in structure and specialised as re- 

 gards their function. Some cells, 

 for example, are gathered together 

 to form organs, possessing the 

 special function of forming the di- 

 gestive juices and of carrying out 

 the digestion of the food taken into 

 the body. Other groups of cells are 

 transformed into muscles, and are 

 concerned in bringing about bodily 

 movements. Other cells, again, 

 form organs, such as the eye. 

 Coordination of Activities 



The development of separate 

 organs, each having its character- 

 istic function, implies division of 

 labour, and this, in an animal as in 

 a community, usually leads to 

 greater efficiency. But, although 

 the main function of the cells of 

 the various organs of a highly 

 developed animal consists in carry- 

 ing out digestion, excretion, or 

 movement, as the case may be, 

 the cells still possess the power of 

 building up their protoplasm, and 

 require food and oxygen both for 

 this purpose and for the perform- 

 ance of their special function. 

 Hence the effective working of the 

 different organs, and, indeed, of the 

 body as a whole, depends upon co- 

 ordination of their activities. The 

 muscles, for instance, would quick- 

 ly cease to act, if the digestive 

 system failed to carry out its 

 functions, or if the lungs or circu- 

 latory system failed to supply the 

 muscles with nutritive materials 

 and with oxygen. In this respect 

 the body resembles a highly civi- 

 lized community, whose well- 

 being depends not only on division 

 of labour, but also on the closest 

 cooperation between the different 

 sections of the community. 



_A further outcome of increasing 

 complexity of structure and spe- 



6 i 34 



cialisation of function in the higher 

 animals is that, as regards their 

 functions, the different organs 

 fall into two main groups. One 

 group is primarily concerned with 

 providing for the nutritive re- 

 quirements of the body, with the 

 supply of oxygen, and with the 

 removal of waste-products from 

 the body. The other group of 

 organs is responsible for bringing 

 about the reactions of an animal 

 to changes hi its surroundings. All 

 the higher animals are provided 

 with muscles, and these possess 

 the power of altering their shape, 

 thereby bringing about movement 

 of part or the whole of the body ; 

 and such movements form the only 

 means by which an animal or 

 man can enter into communica- 

 tion with the outer world. Speak- 

 ing is carried out by movements of 

 muscles, all gestures are brought 

 about by muscular movement, and 

 running, walking, and so forth are 

 effected by muscular movement. 

 Nerves and Muscles 



In the normal animal, however, 

 every muscular movement is con- 

 trolled by the central nervous 

 system, which consists of the 

 brain and spinal cord ; and these 

 are connected with the muscles by 

 delicate threads called nerves. 

 Hence every movement of the body 

 is normally dependent on, and is 

 an indication of, the activity of the 

 brain or spinal cord. If the nerves 

 passing from the nervous system 

 to any particular muscle are 

 destroyed, that muscle becomes 

 useless and is said to be paralysed. 



It is clear, therefore, that the 

 range and variety of the movements 

 which an animal can carry out is 

 proportional to the development 

 of its muscular and nervous sys- 

 tems. The brain is also con- 

 nected by means of nerves with 

 the surface of the body, with the 

 eye, and with the ear ; and a ray of 

 light falling into the eye, or an 

 object touching the skin, causes 

 an impulse to pass to the brain, 

 which may respond to this stimu- 

 lus by setting in action certain 

 muscles. This sequence of events 

 occurs, for example, when the 

 hand is suddenly drawn away from 

 a hot object placed in contact with 

 it. Since the ability of an animal 

 to respond effectively to the stimuli 

 constantly reaching the body from 

 without depends upon the capacity 

 of the nervous system to bring 

 about muscular movements, the 

 development of its nervous system 

 is the measure of an animal's ' 

 position in the scale of evolution. 



It is evident, then, that the stu- 

 dent of physiology must proceed 

 along three main lines of inquiry. 

 In the first place, it is necessary 



PIACENZA 



for him to discover as accurately 

 as possible the functions of each 

 organ of the body and the condi- 

 tions under which these functions 

 are carried out. In the second 

 place, he is called upon to study 

 how the animal reacts to the 

 changes constantly taking place in 

 its surroundings. Lastly, he must > 

 ascertain how the activities of the 

 different organs of the body are 

 linked together and coordinated 

 so as to promote the highest 

 efficiency of the body as a whole. 



In the animal world structure 

 and function go hand in hand, 

 and observation has shown that, 

 if a similar structure or organ is 

 found in two types of animals, the 

 mam function of that organ will 

 be the same in the two animals. 

 The study of the functions of the 

 lower animals, therefore, not only 

 adds to the sum of knowledge, 

 but is of supreme importance from 

 a practical point of view, since it 

 throws light on the functions of 

 the human body. 



Bibliography. General Physiology, 

 M. Verworn, Eng. trans. F. S. Lee, 



1899 ; Lessons in Elementary Phy- 

 siology, T. H. Huxley, new ed. 



1900 ; Textbook of Physiology, M. 

 Foster, 7th ed. 1907 ; Elements of 

 Human Physiology, E. H. Starling, 

 8th ed. 1907 ; Handbook of Phy- 

 siology, W. D. Halliburton, 9th ed. 

 1909 ; The Body at Work, A. Hill, 

 1909 ; The Human Body, A. Keith, 

 1912. 



Physostigmine OB ESEKINE. 

 Substance obtained from the 

 calabar bean (Physostigma veneno- 

 sum) and used for various affections 

 of the eye. See Calabar Bean. 



Piacenza. Prov. of N. Italy, in 

 Emilia. It lies S. of Milan, E. of 

 Pa via, and W. of Parma. The sur- 

 face is level in the N. and moun- 

 tainous in the S. Its area is 967 

 sq. m. Pop. 267,000. Prow. 

 Pe-achentsa. 



Piacenza. City of Italy, the 

 ancient Placentia. The capital of 

 the prov. of the same name, it 

 stands on the right bank of the 

 river Po, just below the influx of 

 the Trebbia, and is a junction 92 

 m. by rly. N.W. of Bologna and 

 36 m. W.N.W. of Parma. It con- 

 tains the 13th century Palazzo Com- 

 munale, the Palazzi dei Tribunali, 

 and degli Scoti, early Renaissance 

 brick and terra-cotta buildings ; the 

 Palazzo Governo, with a famous 

 sundial ; the Palazzo Farnese, a 

 huge structure begun in 1558, but 

 unfinished and now used as a bar- 

 racks; and two episcopal palaces. 



The cathedral, dating from 1122- 

 1233, has a handsome belfry. The 

 church of S. Antonino, the original 

 cathedral, was founded in the 4th 

 century, restored in 903, rebuilt in 

 1104, and altered in 1857. The 



