132 IRRITABILITY 



which produces the breaking down of the complex molecules 

 upon the surrounding molecules is a problem which can only be 

 studied later. Here only one point will be mentioned in advance 

 concerning the intensity of the stimulus. It is apparent from the 

 experiments on the rhizopods, that the greater the intensity of the 

 stimulus the more extensive must be the breaking down of the 

 living substance. A stronger primary stimulation must also 

 secondarily produce a stronger stimulus in the neighborhood. In 

 other words : the conduction of excitation is a function of irrita- 

 bility. The greater the irritability, that is, the greater the number 

 of molecules broken down in a unit of time and space by a stim- 

 ulus of a certain intensity, the greater also is the conductivity of 

 the living system, that is, the stronger, the more rapidly and the 

 further excitation is extended. Conductivity of excitation is, 

 therefore, unthinkable without irritability. Both are inseparably 

 connected. The conclusion forced upon us by this chain of 

 reasoning admits of no argument. Nevertheless the endeavor 

 has been made, because of certain evidence at hand, to show that 

 the property of conductivity could exist without irritability. A 

 number of authors, such as Schiff,^ Erb,~ Griinhagen,^ Effron* 

 Hirschberg^ and G. Weiss,'^ have observed the fact that in spite of 

 a more or less strong decrease of excitability of a stretch of nerve, 

 stimuli applied above this stretch can still produce a conduction 

 of excitation through the affected part. They have concluded 

 from this that it is possible to separate the conductivity from 

 irritability. Erb and G. Weiss have even gone so far as to directly 

 express the opinion that, capability of conduction and irritability 

 involve two different histological elements. In contrast to this, 



1 Schiff: "Uber die Verschiedenheit der Aufnahmsfahigkeit und Leitungsfahigkeit in 

 dera peripherischen Nervensystem." Henle u. Pfliigers Zeitschr. 1866. 



2 Erb: "Zur Patho'ogie und pathologischen Anatomic peripherischer Paralysen." 

 Deutsches Arch. f. Klin. Med. 1869. 



3 Griinhagen: "Versuche uber intermittierende Nervenreizung." Pfliigers Archiv. 

 Bd. 6, 1872. — Funke-Grunhagen." Lehrbuch der Physiologic Bd. I, 1876. 



4Effron: "Beitrage zur allgemeinen Nervenphysiologie." Pfliigers Arch. Bd. 36, 

 1885. 



SHirschberg: "In welcher Beziehung stehen Leitung und Erregung der Nervenfaser 

 zu einander?" Pfliigers .^rch. Bd. 39, 1886. 



6 G. IVeiss: "La conductibilite et I'excitabilite des nerfs." Journ. dc physiol. et de 

 pathol. generale. T. V. 1903.— "Influence des variations de temperature et des actions 

 mechaniques sur I'excitabilite et la conductibilite des nerfs." Ibidem. 



