THE FUNDAMENTAL PHYSIOLOGICAL ACTIONS 25 



It is this disproportion between the excitant (known in Physiology 

 as a stimulus) and the result, which is the essential characteristic 

 of irritability when the term is used in a physiological connection. 

 The granular cells of the blood can take foreign matters into them- 

 selves in exactly the same manner as an Amoeba does; and in this 

 and in other ways, as by contracting into rigid spheres under the 

 influence of electrical shocks, they show that they also are endowed 

 with irritability. 



Conductivity. Further, when an Amoeba or one of these blood- 

 cells comes into contact with a foreign body and proceeds to draw 

 it into its own substance, the activity excited is not merely dis- 

 played by the parts actually touched. Distant parts of the cell also 

 cooperate, so that the influence of the stimulus is not local only, 

 but in consequence of it a change is brought about in other parts, 

 arousing them. This property of transmitting disturbances is 

 known as conductivity. 



Finally, the movements excited are not, as a rule, random. 

 They are not irregular convulsions, but are adapted to attain a cer- 

 tain end, being so combined as to bring the external particle into 

 the interior of the cell. This capacity of all the parts to work to- 

 gether in definite strength and sequence to fulfil some purpose, is 

 known as coordination. 



These Properties Characteristic but not Diagnostic. These 

 four faculties, irritability, conductivity, contractility, and coordi- 

 nation, are possessed in a high degree by our Bodies as a whole. 

 If the inside of the nose be tickled with a feather, a sneeze will 

 result. Here the feather-touch (stimulus) has called forth move- 

 ments which are mechanically altogether disproportionate to the 

 energy of the contact, so that the living Body is clearly irritable. 

 The movements, which are themselves a manifestation of con- 

 tractility ', are not exhibited at the point touched, but at more or 

 less distant parts, among which those of abdomen, chest, and face 

 are visible from the exterior; our Bodies therefore possess physio- 

 logical conductivity. And finally these movements are not random, 

 but combined so as to produce a violent current of air through the 

 nose tending to remove the irritating object; and in this we have 

 a manifestation of coordination. Speaking broadly, these proper- 

 ties are more manifest in animals than in plants, though they are 

 by no means absolutely confined to the former. In the sensitive 



