Seasonal Changes in Frog's Muscles and Their Bearing on Clasping Reflex

Sommerkamp 1 showed that different striated muscles reacted differently to contracture producing substances such as acetyl choline, nicotine, etc., and explained his results by the assumption that certain muscle fibers (tonus fibers) reacting specifically to contracture producing substances are unequally distributed in different muscles. It is apparent that these investigations have great importance in the study of tonus. Therefore experiments were carried out in which the isometric tension of the flexors of the forelimb was determined in male and female frogs (Rana esculenta). Acetyl choline (1:10,000), KSCN (0.113M) and veratrin (1:1,000,000) were used during and after breeding season. The results are summarized in Tables I and II. While the isometric tension set up by KSCN expressed in percentage of the tetanus tension produced by a just maximal current is practically identical in males and females the experiments with acetyl choline show that the muscles of male frogs react specifically. The tension in males averages 13% and in females 3.2%. It is interesting that several weeks after breeding season an intermediate value averaging 5.6% is obtained from males.

The isometric curve of flexors of the forearm which were poisoned with veratrin sulphate revealed the specific reaction of the male muscles during breeding season in a still more striking manner. When stimulated with a just maximal faradic current the tension of the slow contracture beginning immediately after the twitch was regularly greater than the twitch tension in males during breeding season; in females the contracture tension was the lower. In these experiments again an intermediate reaction was observed in males several weeks after breeding season. The specific reactions are restricted to the flexors of the forearm since other muscles like M. gastrocnemius even in the breeding season react alike in males and females.