282 University of California Publications in Zoology [Vol. 11 



TABLE XI 



Influence or Chloeetone Upon the Dukation or Swimming Responses 

 Evoked by Repeated Contact Stimulation 



7. Carbon Dioxide 



It is known that oxidation and destruction of carbohydrate 

 in the body result in the formation of at least two waste sub- 

 stances, both of an acid character, namely, carbon dioxide and 

 lactic acid. These two products of metabolism are considered 

 important factors in causing fatigue in skeletal muscle. For 

 them Lee (1910) has suggested the term "fatigue substances." 

 This investigator (1907) found in the frog that upon injecting 

 a 0.07 per cent sodium chloride solution containing considerable 

 quantities of carbon dioxide into the muscles of the leg "it will 

 be observed that the curves of the muscle under the influence 

 of carbon dioxide, from the 1st to the 151st contraction inclusive, 

 are higher than those of the normal muscle, — in other words, 

 carbon dioxide exerts at first an augmenting action. From the 

 two hundred and first contraction on the fatiguing effect is 

 manifest. ' ' 



A leech placed in 100 cm. of tap water + 100 cm. of carbonated 

 water was at first excited to marked activity. Within five min- 

 utes the animal showed depression to the extent that it was 

 incapable of progressive movement. The specimen was imme- 

 diately removed to a dish of fresh water. It at once began 

 movements of the anterior end, and five minutes later performed 

 swimming movements of a partially co-ordinated character. This 

 was at ten o'clock, and seven minutes after the animal swam 

 actively about in the dish upon being stimulated, though dis- 

 playing a condition of lower tonus. At twenty minutes past ten 

 the leech appeared entirely normal in its responsiveness. 



