36 BIOLOGY: GENERAL AND MEDICAL 



These examples of results disproportionate to their 

 respective causes have found their way into many text- 

 books and unfortunately confuse the student, for they 

 apply with accuracy only to conditions that may be 

 compared to the charge in the gun or the vapor tension 

 in the boiler. Thus, when we examine the conditions 

 found among living things in which such disproportions 

 are noted, and an explosive disturbance follows what 

 seems to be a trifling stimulus, we find that instead of a 

 simple reaction we have to deal with some complicated 

 mechanism in which the transmission of the impulse 

 from the cell stimulated to many other .cells, results in 

 an effect which is the sum of many separate stimulations. 



This is the case with the Mimosa or sensitive plant 

 whose leaves all close when a few pinules are touched, and 

 with Dionoea, or the " Venus' fly-trap," in which, when a 

 few hairs are touched, the leaf closes, entrapping the 

 offending insect. The same condition is found in the 

 higher animals whose nervous systems are so coordinated 

 as to act reflexly, the prick of a pin or some other slight 

 stimulation sufficing to set in motion a series of stimu- 

 lations terminating in the involuntary and convulsive 

 movement of a muscle, a group of muscles controlling 

 a member, or even most of the muscles of the body. 



That such explosive reactions are exceptional, and 

 that many of the manifestations of irritability are appre- 

 ciable only after the lapse of considerable time, and then 

 only through slight changes, will soon become apparent. 



Stimulations calling forth a normal expenditure of 

 energy, the loss of which can be amply compensated for 

 by the nutritive function, may continue indefinitely, as 

 is evidenced by the continuous operation of all those 

 stimuli that have to do with normal growth and function. 

 Those calling for excessive expenditures of energy soon 

 exhaust vitality, and throw the living substance into an 

 inactive state known as rigidity or "tetanus." If, after 

 the development of this state, time be given for the 

 metabolic functions to restore the integrity of the proto- 



