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AN AMERICAN TENT-BOOK OE PHYSIOLOGY. 



contractions, the " staircase contractions." These phenomena repeat themselves 

 in the second part of the experiment, that following the interval of rest. The 

 contractions at the beginning- of the second series were not so high as those at 

 the end of the first series, though somewhat higher than those seen at the 

 beginning of the first series; the rest of five minutes was not sufficient to 

 entirely do away with the stimulating influence of the preceding work. The 

 contractions of the second series took the following course: The first four 

 introductory contractions gradually declined, then came the staircase contrac- 

 tions, which continued to rise until the 100th contraction, when a gradual 

 lessening of the height of the contractions began. This decline continued 



6fi contractions. 



Rest. 1-30 



400 



500 



G00 



700 



S00 



900 



1000 



1100 



1200 



1300 



1100 



1500 



1(300 



1700 



Fig. 46.— Effect of fatigue on the height of muscular contractions. The figure is a reproduction of 

 parts of a record of over 1700 contractions made hy an isolated gastrocnemius muscle of a frog. The con- 

 tractions were isotonic, the weight heing about 20 grams. The stimuli were maximal breaking induction 

 shocks, and were applied directly to the muscle, at the rate of 25 per minute. Between the first group of 

 66 contractions and the following groups a rest of five minutes was given; after this rest the work was 

 continued without interruption for about one and a half hours. The second group of contractions, that 

 immediately following the period of rest, contains the tirst twenty contractions of the new series; the 

 next group the 100th to the 110th ; the next the 200th to the 210th, and so on. 



throughout the long series of more than 1700 contractions given in the record, 

 and, had the experiment been continued, would have undoubtedly gone on 

 until the power was completely lost. The curve of fatigue was not a straight 

 line, but fell somewhat more rapidly during the early part of the work than 

 toward the end. 



That the peculiar changes in the height of the contractions which occur in 

 the early part of an experiment such as that which we have described are not 

 abnormal, and the result of the artificial conditions under which the work is 

 done, is shown not only by the fact that they are observed when a muscle 



