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. I 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 fibriiiogen. How the nature of the 

 contact can influence the leucocytes is still a mystery. One 

 might think of surface tension phenomena or the formation 

 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: 



Sodium-citrate solutions 

 Sodium-fluoride solutions 



Air 

 CO 2 

 Oil 



From { Sodium-oxalate solutions To -! 2n sugar solution 



Sodium-carbonate solutions 

 etc. (see above) 



Glycerin 



Chloroform 



Toluol 



