SECONDARY CONTRACTION. 559 



every time the latter, B, contracts, the frog's muscle, A, connected with the nerve 

 also contracts. 



If the nerve of a frog's nerve-muscle preparation be placed on a contracting 

 mammalian heart, then a contraction of the muscle occurs with every beat of the 

 heart (Matteucci, 1842). The diaphragm, even after 

 section of the phrenic nerve, especially the left, also con- 

 tracts during the heart-beat (Schiff). This is the 

 "secondary contraction" of Galvani. 



Secondary Tetanus. Similarly, if a nerve of a nerve- 

 muscle preparation be placed on a muscle which is 

 tetanised, then the former also contracts, showing 

 "secondary tetanus" (du Bois-Reymond). The latter 

 experiment is regarded as a proof that, during the pro- 

 cess of negative variation in the muscle, many successive 

 variations of the current must take place, as only rapid 

 variations of this kind can produce tetanus by acting on 

 a nerve continuous variations being unable to do so. 



Usually, there is no secondary tetanus in a frog's nerve- * 5# . 



muscle preparation when it is laid upon a muscle which is Secondary contraction. The 

 tetanised voluntarily, or by chemical stimuli, or by poisoning sciatic nerve of A lies on B ; 

 with strychnin (Bering, Kilhne) ; still, Loven has observed E, electrodes applied to the 

 secondary strychnin tetanus composed of six to nine shocks per sciatic nerve of B. 

 second. Observations with a sensitive galvanometer, or Lippmann's capillary electrometer (fig. 

 400), show that the spasms of strychnin poisoning, as well as a voluntary contraction, are dis- 

 continuous processes (Loven, \\ 485). 



Biedermann observed that striped muscle, under the influence of the vapour of ether, passes 

 into a condition in which it shows no obvious change of form or movement when it is 

 stimulated, whilst at the spot stimulated, there are galvanometric variations of the same strength 

 as occurred during stimulation before the action of the ether. Owing to the abolition of the 

 power of conductivity, they can only manifest themselves locally. 



[Secondary Contraction from Muscle to Muscle (Kilhne). If 5 mm. of one end 

 of the sartorius of a curarised frog be laid upon a corresponding 5 mm. of the other 

 sartorius, so that both muscles are in line, and if the surfaces of contact be pressed 

 together, either by an ebonite press or other means, on stimulating the free end 

 of one of the muscles either electrically, mechanically, or chemically the other 

 muscle also contracts, and if the first one be tetanised, the second one also is thrown 

 into tetanus. The experiment may be repeated with five or six muscles in line. 

 The conduction is interrupted at once by ligature of the muscle. The second 

 muscle contracts, because it is stimulated directly by the action-currents of the 

 contracting muscular fibres. The effect is prevented by introducing, between the 

 overlapping ends of the muscle, a thin plate of gutta-percha, tinfoil, or any insulator. 

 This experiment of Kiihne's shows us how important a role electrical phenomena 

 play in connection with muscular contraction. Secondary contraction from nerve 

 has long been known.] 



Negative Variation in Nerve. If a nerve be placed with its transverse section 

 on one non-polarisable electrode, and its longitudinal surface on the other, and if it 

 be stimulated electrically, chemically, or mechanically, the nerve-current is also 

 diminished (du Bois-Reymond). This negative variation is propagated towards 

 both ends of a nerve, and is composed of very rapid, successive, periodic, interrup- 

 tions of the original current, j ust as in a contracted muscle (Bernstein). Hering 

 succeeded in obtaining from a nerve, as from a muscle, a secondary contraction or 

 secondary tetanus. The amount of the negative variation depends upon the 

 extent of the primary deflection, also upon the degree of nervous excitability, and 

 on the strength of the stimulus employed. The negative variation occurs on 

 stimulating with tetanic as well as with single shocks. The negative variation 

 is not observed in completely uninjured nerves. 



