FACTORS VARYING THE CHARACTER OF THE CONTRACTION 83 



10 seconds, may not be able to induce fatigue. It is also essential to 

 use maximal weights, because the effects of small weights are generally 

 compensated for within a very short time. The interval which should 

 elapse between two successive ergograms showing complete normal 

 fatigue, is close to 2 hours. If a muscle is made to contract before it has 

 fully recovered from a preceding exertion, it may be more severely 

 injured than if it had been forced to lift excessive loads to begin with. 

 Practically no two ergograms are alike, because every person presents 

 certain individual peculiarities which are dependent upon his physio- 

 logical condition. Thus, pronounced mental or bodily fatigue from 

 such causes as loss of sleep, anemia, lowered nutrition, etc., is prone to 

 produce a more rapid exhaustion of the muscle than could possibly be 

 obtained in a perfectly robust person. Practice and training enhance 

 the power of a muscle, and this end may also be attained by augment- 

 ing the local or general circulation by drugs, massage, baths as well as 

 by the ingestion of certain foods, such as sugar. . 



CHAPTER VIII 



THE CHARACTER OF THE CONTRACTION OF SMOOTH 



MUSCLE 



The Tonicity of Smooth Muscle.- The organs and structures con- 

 taining non-striated muscle cells are innervated by the autonomic 

 system and are therefore not under the direct control of the will. 

 In fact, they are in a way independent of the cerebro-spinal system, 

 because their function continues even after they have been separated 

 from it. Herein lies the implication that they are well equipped with 

 intrinsic nervous elements which are capable of controlling their action 

 even in the absence 1 of the higher centers. If the bladder or a segment 

 of the stomach or intestine is excised and suspended in a chamber 

 under proper conditions of moisture and tempeiature, it may easily 

 be observed that it retains its tonus and even executes spontaneous 

 contractions. The latter may be of myogenic or neurogenic origin, 

 although Schultz 1 claims that they arise solely in consequence of exci- 

 tations of local nervous elements and are therefore reflex in their 

 character. In accordance with this statement, the ordinary condition, 

 of tonus of non-striated muscle may be said to have both a myogenic 

 and neurogenic cause, the former giving rise to the ordinary elastic 

 state of its substance, and the latter to periodic excitations which are 

 relayed to it by way of definite reflex paths. Considered in this light, 

 the spontaneous contractions of smooth muscle are mere variations 

 in the neurogenic tonus. 



1 Archiv fur Physiol., Suppl., 1903. 1; also see: Grutzner, Ergebnisse der 

 Physiol., iii, 1904, 2. 



