28 PHYSIOLOGY CHAP. 



all the details of its appearance under the microscope. This is 

 easily accomplished if a fresh muscle from an insect's leg is 

 dropped into absolute alcohol or solution of osinic acid. These 

 reagents excite a series of waves in the muscle fibre, and fix it at 

 the same time, so that on teasing out some bundles of fibres for a 

 few minutes and examining them under the high power, the so- 

 called "fixed wave of contraction " can be seen in the form of 

 nodes or fusiform swellings. In some fibres it is also possible to 

 see the so-called " lateral waves," due to contraction of one surface 

 of a fibre which is relaxed on the opposite side, and intermediate 

 parts between the two surfaces show gradations of all the 

 intermediate stages between the phases of contraction and of 

 relaxation. 



Engelmann (1878) made the most important contributions to 

 this subject. He found in the muscle fibres of an insect (Thele- 

 phorus melanurus) treated as above, that the optical properties 

 and the breadth of the isotropous and anisotropous bands altered 

 inversely to the changes in the form of the fibres during contrac- 

 tion. As shown by Fig. 21 the isotropous layers become as a 

 whole more refracting, i.e. more compact and darker, while the 

 anisotropous layers become less refractive, i.e. more fluid and 

 lighter. The breadth of both layers diminishes during contraction, 

 but more rapidly in the isotropous than in the anisotropous bands, 

 so that the latter increase in volume at the expense of the former. 

 Thus, according to Engelmann, we must assume that during 

 contraction the anisotropous substance subtracts water from the 

 isotropous. 



The same fact is more evident in Fig. 22, which represents a 

 lateral contraction wave, observed by Eollet near a motor end-plate. 



Ranvier (1880) employed an ingenious method for determining 

 which bands of the sarcoplasm contracted, and which behaved 

 passively, when stimulated. He put two muscles of a frog or 

 rabbit into a condition of absolute isometry, and then fixed them 

 by absolute alcohol while one was inactive, the other in tetanus 

 produced by an induced current. On then comparing the muscles 

 under the microscope, he found a reduction in the breadth of the 

 dark anisotropous discs in the fibres of the tetanised musclp, which 

 were now perceptibly equal to the clear isotropous discs, while 

 in the inactive muscle they were considerably broader. He 

 further pointed out that there was in the fibres of the tetanised 

 muscle a considerable increase of the interfibrillar sarcoplasm, 

 which appeared to break up the fibre into fibrils. 



According to Ranvier, therefore, the layers of anisotropous 

 substance diminished in volume. Contrary to Engelmann's 

 results, water does not pass from the isotropous to the anisotropous 

 substance during tetanic tension, but diffuses from the latter into 

 the interfibrillary substance. 



