GENERAL HISTOLOGY IOQ 



it is important to notice the differences between the 

 t\vo kinds of movement. The distinctions , 



lie in the direction and in the intensity of the 

 movement. A mass of protoplasm has the 



' eC 



capacity to move hither and thither in all 

 directions, because internally the most com- 

 plete change of position of the smallest mole- 

 cules with reference to each other is possi- 

 ble. All muscles and correspondingly also 

 their separate elements, the muscle-fibres and 

 muscle-fibrils, possess, on the contrary, the 

 capacity of shortening only by a correspond- ^ac^d^t a C "! 



, /T^- (After Merkel.) 



ing simultaneous increase in diameter (Fig. 

 45); they can therefore accomplish motion only in a defi- 

 nite direction, viz. , in the direction of the axis of the muscle. 

 The muscle-substance consequently is more limited in its 

 movement than is protoplasm, but on the other hand it has 

 the advantages of greater energy and greater rapidity. 

 An observer conversant with the nature of the different 

 kinds of motion is able to decide with considerable ac- 

 curacy, from the intensity and rapidity, whether in a given 

 case a movement has been brought about by the agency of 

 protoplasm, or by the contractile substance in the narrower 

 sense (muscle-substance). 



The Formation of Muscle-substance. These phy- 

 siological considerations demonstrate that protoplasm and 

 the contractile substance are morphologically different 

 things, and that therefore one must distinguish sharply 

 between formative cells, or muscle-corpuscles, and the prod- 

 uct of these cells, or contractile substance, just as in the case 

 of connective tissue, between the connective-tissue corpus- 

 cles and the connective-tissue fibrils. This distinction 

 actually occurs, but optically it is not equally demonstra- 

 ble, for the reason that in histology it is not brought into 

 prominence in the mass, as it should be. In animal his- 

 tology there are recognized two kinds, it might even be said, 

 t\vo stages, in the formation of muscle-substance, the Jionio- 

 gcncous, or smooth, and the cross-striated. Since the former 



