XIIl] STRIATED MUSCLE 105 



NOTES. 



Living fibres. Thin muscles may be pinned out whole over a 

 ring of cork ; the mylo-hyoid of the frog and the sub-cutaneous 

 muscles of the face arid neck of a rabbit may be so treated. 



With thick muscles a few fibres should be torn out and 

 mounted in aqueous humour, fresh serum, or NaCl '75 p.c. ; the 

 fibres of insects are best mounted in the blood of the animal. 

 According to Nasse, a 1 to 1*5 p.c. NaCl solution is better than 

 a '75 p.c. solution for certain muscular fibres (e.g. of flies). In 

 some fibres contraction waves may be seen ; as the fibres die one 

 part of the fibre may be seen to contract, and the contraction 

 to spread from this spot towards the end of the fibres : the 

 behaviour of the various bands should then be carefully noted. 



Fixing and isolating agents. To observe the various bands 

 the muscle should be stretched before being placed in the re- 

 agent. This may be done conveniently by cutting out the parts 

 to which the muscle is attached, and pinning out the attachments 

 of the muscle over a ring of cork ; or by placing the whole animal 

 in the reagent and selecting the extended muscles. 



The best reagent to use is different in different cases : the 

 following reagents generally give good results for teased speci- 

 mens ; absolute alcohol ; osmic acid '5 p.c. for five to thirty 

 minutes, then alcohol ; a concentrated aqueous solution of 

 salicylic acid this, like alcohol, coagulates the proteids of the 

 muscle, but it also swells up the connective tissue ; 30 p.c. 

 alcohol. When a muscle cannot conveniently be extended, a 

 concentrated aqueous solution of boracic acid may be used ; this 

 does not coagulate the proteids of the muscle, and causes little or 

 110 shrinking (Nasse). For sections, any of the usual hardening 

 agents will serve. 



With insects, e.g. cockroach and dytiscus, the reagent rnay 

 be injected into the body cavity, or the insect, e.g. a caterpillar, 

 may be plunged whole in the reagent. In both of these cases 

 some fibres may usually be found with fixed local contraction 

 waves ; a convenient way of obtaining fixed contraction waves is 

 in many cases by tearing out a leg and plunging the protruding 



