118 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



above experiment, and the resulting condition of continued contraction caused 

 first incomplete and finally complete tetanus. 



Although frequent excitations appear to be essential to the development 

 of contracture, it is not to be considered a fatigue effect, since the contracted 

 state which it produces may be increasing at the time that fatigue is lessen- 

 in"- the height of the ordinary contraction movements, and since the form of 

 contraction peculiar to contracture is itself seen to lessen as fatigue becomes 

 excessive. Both of these facts are illustrated in Figure 50, but are more 

 strikingly shown in Figure 51, in which a more rapid rate of excitation was 

 used. The effect of fatigue to prolong muscular contractions and the relation 

 of contracture to fatigue effects will be considered later (sec p. 130). 



The record in Figure 51 shows many points of interest : a to b, a rapidly 



Fig. 49.— Effect of frequent stimuli to gradually produce incomplete tetanus. Series of isotonic con- 

 tractions of a gastrocnemius muscle of a frog, excited once every two seconds by strong breaking induc- 

 tion shocks. Only a part of the record is shown, 70 contractions have been omitted between the end of the 

 section marked o and the beginning of section b, and 200 contractions between the end of section band tin 

 beginning of c. The increase in the extent of the relaxations seen at the close of the record was due 

 to the slowing of the rate of excitations at that time. 



developing staircase, which is accompanied by a rising of the base line, which 

 indicates that contracture began to make itself felt from the moment the work 

 began ; b to c, a rapid and then a gradual fall in the height of contractions 

 due to fatigue effects ; c to d, a rise in the top of the curve in spite of the 

 lessening height of the contractions, due to the increasing contracture ; d to e, 



