700 STUDIES IN GENERAL PHYSIOLOGY 
tions, although the hydrostatic pressure on the surface of the 
muscle was increased. 
It thus seems to me that none of the known forms of 
muscular irritability suffices to explain the phenomena 
with which we are dealing. We have before us an appar- 
ently new form of muscular irritability, probably contact- 
irritability. 
Contact-irritability is a very general form of irritability 
among plants and lower animals. J need only to remind the 
reader of the phenomena of stereotropism and of the fact 
that by mere contact-effects a polyp of a campanularia can 
be transformed into a stolon. But contact-irritability cer- 
tainly exists among certain cells of vertebrates, for example, 
the leucocytes. The nature of the body with which leuco- 
cytes come into contact determines whether or not they give 
off fibrin ferment and cause coagulation of the blood or other 
liquids which contain fibrinogen. How the nature of the 
contact can influence the leucocytes is still a mystery. One 
might think of surface tension phenomena or the forma.ion 
of double electric layers at the surfaces in contact. 
If the phenomena described in this paper were really con- 
tact-phenomena, a further search should reveal that only a 
change of contact from certain bodies to other bodies can 
cause contractions of the muscle. 
I have begun experiments in this direction, and have thus 
far found the following facts: 
Contractions occur when the muscle passes: 
; ( Air 
{ Sodium-citrate solutions | CO, 
| Sodium-fluoride solutions Oil : 
From ; Sodium-oxalate solutions To ~ 2n sugar solution 
| Sodium-carbonate solutions Glycerin 
li etc. (see above) Chloroform 
Toluol 
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