4 INTRODUCTION 



significance and it is sufficiently obvious that instruments and machines 

 widely differing in shape and function may be constructed from similar 

 masses of iron or brass. 



In explaining the relations between cause and effect, Physiology, like 

 every other science ; must determine the nature and properties of the 

 different parts affected, as well as the accompanying external factors 

 which may be involved. Both the character of the stimulus to action 

 and the necessary mechanical means by which the resulting phenomenon 

 is effected require to be known, and the more thoroughly a particular 

 phenomenon is investigated, the more numerous are found to be the various 

 related factors which originate and influence it. Nevertheless, an accurate 

 knowledge of the more immediate causes which produce a given result 

 often permits a further and deeper analysis to be made, and may thus 

 afford a satisfactory preliminary explanation of the phenomenon in 

 question, which may serve as a sound basis for further research. Science 

 is based solely on properties and facts ascertained by experiment and 

 observation, that is to say, on a knowledge that under given conditions 

 certain results must necessarily be obtained. The physiologist who deter- 

 mines empirically the part played by each of a number of co-ordinated 

 factors in producing a given phenomenon, does no more than the physicist, 

 who frequently uses a quantity which is capable of being resolved into 

 factors as the starting-point for a research, or the mathematician, who 

 deduces logical conclusions from axioms which he has himself propounded. 



We are proceeding therefore by a perfectly scientific method when 

 we explain certain movements as being due to the combined action of 

 tissues, or to a disturbance of the relation between the elasticity of the 

 cell-wall and the osmotic pressure which stretches it. Similarly the phe- 

 nomenon of contractility, or the union of spermatozoid and ovum, may 

 be safely used as a sure foundation for further and deeper studies into 

 the nature of life. 



Every scientific research, in its groping for ultimate causes, brings 

 us to complex characters and properties, the entities of scholastic philo- 

 sophy, which we are unable to further resolve. Cohesion, elasticity, 

 gravity, are all regarded as fundamental properties of matter, although 

 it is not impossible that the atom, and hence also its most essential 

 attributes, may be capable of being resolved into still more elementary 

 parts. Physiology, therefore, stands on precisely the same basis as any 

 other science, although it necessarily accepts complex entities and pro- 

 perties as simple ones as factors, that is to say, which at present cannot 

 be further resolved, since the phenomena of life cannot be referred to 

 the interaction of atoms and different kinds of energy as in the domain 

 of Chemistry and Physics. 



It is therefore not surprising that Physiology should be unable to 



