42 ELECTRO-PHYSIOLOGY CHAP. 



as (N), corresponding with Engelmann's accessory discs (" Ncbcn- 

 scheiben") (Schema II, Fig. 27). 



Finally (Schema ///), the dark band (N) may appear in the 

 middle of the clear segment (J), so that Dobie's line (Z) is 

 bordered directly on either side by a clear line (E), followed 

 by (N), and then by another clear line (J), so that the entire 

 system of bands in a fibre-segment enclosed between two Dobie's 

 lines (Z) is as follows : (ZENJQJNEZ) ; the next simplest 

 case is (Z N J Q J N Z) ; the simplest of all (Z J Q J Z). It 

 is important to remember that none of these several systems of 

 striae can be regarded as characteristic of all muscle-fibres in any 

 particular species of animal. On the contrary, the three conditions 

 of striation indicated in the figures may occur in one and the same 

 fibre, and merge into one another, as shown by Engelmann in the 

 muscles of insects in particular. This effect is due in the first 

 place to different conditions of contraction in the fibres ; the most 

 complicated kind of cross-striation always corresponding with the 

 greatest relaxation of fibre. This by no means excludes the possi- 

 bility of specific varieties of striation ; all the observations tend 

 to show that if it were possible to investigate the muscle-fibres 

 of different animals, or the different muscle-fibres of the same 

 animal, when perfectly relaxed, or at the same degree of exten- 

 sion, they would present very different appearances. 



The reaction of striated muscle-fibres, or individual layers of 

 fibrils, and of the sarcoplasm, to different reagents, is extremely 

 interesting both morphologically and physiologically, the differ- 

 ences exhibited being no less striking than in regard to optical 

 properties. This is plainly expressed by the different colorability 

 of the individual segments. If the transverse section, or the 

 entire muscle -fibre, is appropriately treated with haematoxylin, 

 we find that only the contractile, fibrillated substance of the 

 muscle-columns stains in the first case, and not the interstitial 

 sarcoplasm. On comparing good haematoxyliii preparations of 

 muscle-fibres in longitudinal section, it is evident that only the 

 segments (Q), (N), and (Z) are stained, while the intermediate spaces 

 between them (i.e. the sarcoplasm) and the striaB (h), (J), and (E) 

 are almost or wholly unstained. 



It has been shown that the gold chloride method under certain 

 conditions gives an opposite reaction ; the sarcoplasm only stains, 

 while the contractile fibrils embedded in it remain uncoloured. 



