218 



PRACTICAL PHYSIOLOGY. 



[XXXIX. 



Suppose the slider to be pushed as far to the left that the axis, a, just lies 

 opposite to the collar, r a point which is adjusted on the apparatus then 

 the tension of the muscle is nil. On moving the slider with the hand towards 

 the right, so that the weight, P, acts on points of the lever more and more 

 remored from a, then the tension of the muscle increases steadily, when the 

 writing point, p, records the curve of extension, p, on a horizontally placed 

 and stationary wooden board or glass plate covered with smoked glazed paper. 

 In using the apparatus, board, slot, and slider are placed horizontally, the 

 weight, P, is not applied directly to/, but to the latter the weight is attached 

 indirectly by means of a cord which passes over a pulley. 



Apparatus. Blix's myograph, induction coil arranged for repeated shocks, 

 the electrodes being directly connected with the muscle. The best prepara- 

 tion to use is the double semi-rnembranosus and gracilis (Lesson XXIX. 5) 

 placed side by side and firmly attached to the lever. For these muscles taken 

 from a large liana, esculenta a weight of 2 kilos is used, and for the corre- 

 sponding gastrocnemius i kilo. 



\R 



AJ 



Uf 



FlO. 140. Scheme of Blix's Myograph. S, S. Slider ; R R and R' R'. Guides for slider; a, 6. 

 Lever ; A for muscle ; P. Weight ; r. Collar ; 1 1 and ti t^. Guides for collar carrying 

 weight ; p. Recording point. 



(a.) Take a curve of a passive muscle from the point of greatest tension to 

 nil tension. 



(b.) Take a similar curve from a tetanised muscle. Compare the two 

 curves, and it will be found that the curve of extensibility of the passive 

 muscle is less steep than that of the tetanised muscle, i.e., a contracted 

 muscle is more extensible than a passive one. 



(c.) On a tetanised muscle, move the slider so that the tension is increased 

 from nil to the greatest possible, i.e. , the muscle is more and more "loaded," 

 and then reverse this, so that from the greatest tension there is gradually 

 "unloading." The two curves so obtained do not coincide: the latter lies 

 considerably below the former. It would therefore appear, as far as the con- 

 traction is concerned, that it is not a matter of indifference whether the 

 muscle is being gradually "loaded" or "unloaded." 



4. Elasticity of an Artery. Test the elasticity of a strip of aorta in the 

 same way. 



