MUSCLE 261 



we can correlate with their different modes of action. All 

 human muscles belong to the red kind. 



The most efficient muscle-fibres in the animal kingdom are 

 found in insects. This will not surprise anyone who thinks of 

 an insect's power of movement. If a man could jump as many 

 times his own height as a flea can, he would clear the dome of 

 St. Paul's. An ant can drag an object sixty times as heavy 

 as itself, with no wheels beneath it to diminish friction. Under 

 the same conditions a horse cannot drag much more than its 

 own weight. A dragon-fly, it is asserted although we have not 

 met a man who guarantees that he has made the observation 

 will support its heavy body in the air by the rapid vibration of 

 its wings for four-and-twenty hours without alighting. The 

 chirp of a cricket is produced by the rubbing together of its 

 hind-legs. A mosquito sounds its war-cry much in the same 

 way. The pitch of the note proves that the insect's muscles 

 are contracting and relaxing at least 300 times a second. 

 None of these figures must be applied without qualifications 

 in estimating the relative strength of insect and human 

 muscle. Weight for weight, the muscle of a flea is not so much 

 stronger than ours as the figures might lead one to infer. To 

 ascertain the numerical relation, it is necessary to compare the 

 total cross-section of the two chief segments of a flea's leg with 

 the cross-section of the extensor muscles of a man's thigh and 

 calf, and a man's weight with the weight of a flea. Neverthe- 

 less, after all deductions have been made, a considerable balance 

 of superiority lies with the insect as regards the strength of its 

 muscles, their rapidity of contraction, and power of repeating 

 contraction without fatigue. An insect's muscle is the most 

 suitable that can be obtained for microscopic examination. 

 Its pattern is larger and more distinct than that of other 

 animals. That the pattern should be larger is not quite 

 what might have been expected. It would not have sur- 

 prised us had we found the pattern finer in the more effective 

 type. 



Nothing is easier than to mount a specimen of insect-muscle. 

 The large water-beetle (Dytiscus marginalia) is an excellent 

 subject. It is so easily handled. Having cut off the animal's 

 head, a leg is pulled out from the thorax. It is split open with 

 a penknife, and a little of the muscle is dug out from within its 



