722 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



points of this surface, or the longitudinal surface of the muscle and the 

 transverse section, be connected by non-polarizable electrodes with a sen- 

 sitive galvanometer, at the moment of making the contact a deflection 

 of the galvanometer needle will take place, indicating the presence of a 

 galvanic current. The strongest effect is produced when one point of 

 the transverse section and one point of the longitudinal surface are con- 

 nected with a galvanometer ; even single fibres, nevertheless, if brought 

 into connection with a galvanometer also develop galvanic currents. The 

 direction of the current is from the longitudinal section through the con- 

 ducting wires to the transverse section ; within the muscle itself the 

 current passes from the transverse to the longitudinal section. The 

 nearer the one electrode is to the equator and the other to the centre of 

 the transverse section the stronger will be the current, while the current 

 becomes more feeble when one electrode is approached to the outer sur- 

 face and the other to the edge of the transverse section. 



The existence of a muscle current may further be proved by an 

 experiment which is termed the rheoscopic frog. If the gastrocnemius 

 muscle of a frog be prepared with a long piece of sciatic nerve still in 

 connection with it, and the end of the nerve be placed over another 

 excised, fresh gastrocnemius muscle, so as to be in contact with its trans- 

 verse and longitudinal surfaces, contraction of the muscle connected with 

 the nerve occurs at the moment of contact. A single contraction is, 

 however, only produced, but if the nerve be removed from the muscle a 

 second contraction occurs ; thus pointing out that the current circulating 

 through the muscle is a constant current and may serve to stimulate other 

 muscles or nerves at the moment of breaking and making the contact. 

 If a muscle be prepared as before, connected with a galvanometer, and be 

 found to yield a strong galvanic current, if the muscle be then thrown 

 into tetanus by electrical stimulation of the muscle itself, or of its motor 

 nerve, the needle of the galvanometer will be found to swing back to 

 zero, indicating the disappearance of the muscle current ; such a state 

 of affairs is spoken of as the negative variation of the muscle current. 



2. The Applications of Muscular Contractility. — The contractility 

 of muscles serves especially to produce changes in form of the animal 

 body by which single members are thrown out of their condition of 

 equilibrium and changes of location in the animal parts thus produced ; 

 or in the case of the unstriped muscles to diminish the capacity of the 

 various cavities of the animal body. Hence, muscles may be classified 

 into two different groups : those without a definite origin and insertion, 

 and those in which definite origin and insertion are present. To the first 

 group belong the hollow muscles surrounding the urinary bladder, gall- 

 bladder, uterus, heart, intestinal canal, blood-vessels, ureters, etc. In 

 such instances the muscular fibres are unstriped and involuntary and are 



