GENERAL PHYSIOLOGY OE MUSCLE AND NERVE. 141 



In the above experiment 30 grams were added to the muscle after each 

 contraction ; as the weight was increased up to 90 grams the amount of 

 work was increased, with greater weights the amount of work was lessened. 



It is evident that the absolute force of a muscle of a given type will depend 

 not only on the quantity, but also on the arrangement of the microscopic ele- 

 ments of which the muscle is composed. Each element of a fibre lias to stand 

 the strain of the whole fibre ; so the force to be developed depends not on the 

 length of the fibres, but on the number of muscle elements which are arranged 

 side by side, i. e. the absolute force of a muscle will be proportionate to the 

 number of fibres. This can be stated for a muscle with parallel fibres in 

 terms of the cross section of the muscle. In the case of a muscle like the 

 gastrocnemius, where the fibres take an oblique course and are inserted into 

 a common tendon in the middle, the " physiological cross-section " has to be 

 estimated, i. e. the total section taken at right angles to the fibres. Such a 

 muscle is very strong in proportion to its thickness. Rosenthal estimated 

 the absolute force of striated muscles of the frog to be about 3 kilograms per 

 square centimeter, and Hermann l found the absolute force of striated muscle 

 of man to be 6.24 kilograms per square centimeter. 



The physiological work of which a muscle is capable, on the other hand, 

 is dependent not only on the weight which it can lift, but also the height to 

 which the weight can be lifted. All the muscle elements, whether arranged 

 side by side or in chains, influence the result, and for purposes of comparison 

 one can state the capacity of the muscle for work in terms of the unit of 

 bulk, the cubic centimeter, or the unit of weight, the gram. Thus, Fick 

 states the maximal amount of external work of which frog's muscle is 

 capable, as one grammeter per gram of muscle substance. 



From what has been said it is evident that the amount of muscle sub- 

 stance determines the amount of work of which the muscle is capable, while 

 the arrangement of the muscle substance decides the character of the work 

 which it is best fitted to perform. Muscles with long parallel fibres, even 

 though of small sectional area, such as the sartorius, are specially fitted to 

 produce extensive movements of the parts to which they are attached ; and 

 muscles which have a large number of fibres, even though these be short, as 

 in the case of the gastrocnemius, are adapted to move great weights. 



Carvallo and Weiss 2 state that the gastrocnemius muscle of the frog 

 when at rest tears if subjected to a weight of 2 kilos. Its contraction power 

 is estimated to be half a kilo, and when it is contracting its resistance is cor- 

 respondingly increased, so that a weight of 2£ kilos is required to rupture it. 

 The increased resistance can be best explained on the idea that, as Prliiger 

 thinks, a new chemical attraction force is developed in contraction. 



Liberation of Thermal Energy. — Energy leaves the body as mechanical 

 energy only when by its movements the body imparts energy to surrounding 

 objects. Most of the energy liberated within the body leaves it as heat; 



1 Pfluger's Archiv, 1898, Bd. 73, S. 429. 



1 Carvallo and Weiss: Comptes rendus Societe de Biologic, 1899, p. 122. 



