l62 MUSCULAR SYSTEM. [SECT. 87. 



certain circumstances successively advancing and partial contrac- 

 tions are also observed. If the longitudinal and transverse strise 

 be watched during the contraction of muscle, it is not difficult to 

 perceive that the former, should they have been present, disappear, 

 whilst the transverse strise become more distinct and approach each 

 other. From this it may be concluded, that, in the contraction, the 

 principal phenomenon consists in the fibrils becoming shorter and 

 broader, and that by this means the above-mentioned alterations of 

 the fibres are brought about. Moreover, the appearance of trans- 

 verse striae is obviously a physical and not a vital phenomenon, for 

 they are seen in dead muscles ; and, consequently, do not depend 

 upon partial contractions of the fibrils. They seem rather to 

 arise from the fibrils not being homogeneous throughout, but 

 divided into small segments. At the same time, on the opposite 

 hypothesis, they may be explained by supposing that the fibrils are 

 soft threads which, during these contractions, bend in a zigzag or 

 undulating manner, or acquire varicosities. With regard to the 

 sarcolemma, it is probably non-contractile, and serves merely as an 

 enveloping membrane. 



It would not be suitable here to enter at length on the causes 

 which produce muscular contraction. I shall, therefore, confine 

 myself to the following remarks. It is undoubted that the capa- 

 bility of contraction is inherent in the muscular substance, and is 

 only, as it were, called into play by the nerves (see my experi- 

 ments with Urari poison, Virchow, AvcUv. x. which speak strongly 

 in favour of the inherent irritability of muscle). On the other 

 hand it is just as certain, that hitherto no perfectly decisive fact has 

 been brought forward to prove that the striated muscles contract 

 without having been acted on by nerves. What may be the pro- 

 cesses which take place in the fibrils during the contraction is alto- 

 gether uncertain; but, it is to be hoped, that by following out the 

 investigation of the laws of the electric currents in the muscles, in 

 the way so successfully pursued by Du Bois Reymond, some light 

 may be thrown upon this obscure subject. It would be rash to 

 hazard an opinion on the manner in which the nerves act upon the 

 muscles, since the processes which take place in the nerves are as 

 obscure as those in the muscles themselves. This much may, 

 however, be remarked, that since it is shown that in many animals 

 the motor nerves come into contact with the individual fibres only 

 at a few points, and never penetrate into their interior, the nerves 

 must exert their iufluence at a certain distance in the contraction 

 of a muscle. An important observation has been made by 



