BY DR. MICHAEL FOSTER. 367 



At higher temperatures than the normal, the muscle curve 

 is much shortened ; at lower, lengthened. 



3. Poisons : Veratrin, etc. Obs. IY. Arrange the frog 

 as directed for observations on muscles in the living body 

 (Chap. XIX., sec. XI), and having determined the natural 

 muscle curve, inject a small quantity of veratrin (5^-317 grm.) 

 beneath the skin of the back, having previously divided the 

 sciatic nerve near the knee without injuiy to the bloodvessels. 

 Determine the curve at given intervals after the introduction 

 of the poison; the duration of the contraction will be enor- 

 mously prolonged. 



II. The Contraction as a Function of the Stimulus. 



Obs. V. Arrange the nerve muscle preparation in the moist 

 chamber; place the nerve over a pair of electrodes. Load the 

 muscle with about 10 grammes. Arrange for a single induc- 

 tion shock, using in the same series of observations the same 

 either opening or closing shock. Draw an abscissa line on the 

 recording surface. 



Slide the secondary coil as far away as the sliding board 

 will allow from the primary coil. Send a shock through the 

 nerve. If there is no contraction (and most probably there 

 will be none), move the secondary coil some centimetres nearer 

 the primary; repeat the shock. Advance in this way, gradu- 

 ally bringing the secondary coil nearer and nearer to the pri- 

 mary, until the first visible contraction is gained. 



By sliding the seer"''; >il backwards and forwards, 

 accurate^ determine this "minimum stimulus" for the muscle 

 and nerve under the circumstances of the case. 



Advance now steadily on, moving the secondary coil a 

 definite distance nearer the primary each time, and record 

 each contraction as an ordinate on the abscissa line, at dis- 

 tances proportionate to the distances the secondary coil is 

 moved, in a manner similar to Chap. XX., Obs. II. 



The contractions will go on for a while increasing as the 

 strength of the current increases; but at last it will be found 

 that increasing the stimulus no longer increases the contrac- 

 tion, i. e., the ;i maximum contraction" for the muscle and 

 nerve under the circumstances has been reached. Determine 

 accurately the relative positions of the two coils at which this 

 point is reached. 



If with the battery employed to start with the maximum 

 contraction is not reached, increase the number of cells. 



The student in making the above observations is nearly sure 

 to meet with very great irregularities, which will tend very 

 much to confuse the results. These may be partly due to 

 imperfections in the apparatus. He will therefore carefully 

 examine these, and see that everything is in order, and espe- 

 cially that the battery is working steadily. 



