200 THE TISSUE OF THE ORGANIC MUSCLES, BY J. ARNOLD. 



sexual organs it occurs in the oviducts, in the broad and round 

 and in the anterior and posterior ligaments of the uterus. 

 It is by far the most important constituent of the uterus. 

 In the vagina it forms an actual muscular membrane. Its 

 presence in the ovaries, whilst admitted by some, is denied by 

 others. Numerous smooth muscular fibres are found in the 

 nipple and in the surrounding areola, also near the hair follicles, 

 where they have received the name of arrectores pili ; and in 

 the sebaceous and sweat follicles. Finally, the presence of 

 smooth muscular fibres in the ciliary muscle, effecting the con- 

 traction and dilatation of the iris, is to be noted, and I may 

 also refer to the discovery of smooth muscular fibres in the 

 membranes of the egg. 



METHODS OF INVESTIGATION. The more delicate points in 

 the structure of organic muscular fibre are best demon- 

 strated in preparations that have been treated with serum, 

 chromic acid (0*01 per cent.), and solution of gold (01 per cent). 

 The urinary bladder, lungs, and smaller arterial vessels of the 

 frog may be particularly recommended as forming good mate- 

 rial for examination ; but for the isolation of the individual 

 fibres without the application of any reagents, the muscular 

 tunics of the intestine are most appropriate. The means usually 

 employed to effect the separation of the elementary fibres are 

 acetic acid diluted with from 3 to 5 per cent, of water, nitric 

 acid (20 per cent.) and solutions of potash (32 per cent.), 

 all of which act in the same way by dissolving the connecting 

 substance, and thus enabling the muscular fibres to be isolated. 

 Maceration in iodized serum, and in dilute chromic acid (O'Ol 

 to 0*05 per cent.), is in some cases very effective. For the pre- 

 paration of transverse sections, alcohol, chromate of potash, and 

 chromic acid the last two being employed alternately consti- 

 tute excellent hardening agents. If it be desired to examine 

 the muscular fibre in as fresh a state as possible, transverse sec- 

 tions may be prepared from frozen portions of muscle, which 

 have then been placed in serum. Such sections are, moreover, 

 well adapted for being treated with gold, silver, and dilute 

 chromic acid solutions. The course and termination of the 

 nerves are distinctly seen in preparations macerated for from two 



