TISSUES, ORGANS; AND SYSTEMS. 



87 



ti 



exists. These fibre cells arc united by means of a substance 

 which cannot be directly demonstrated, into flattened or rounded 

 cords, the bundles of the smooth muscles j which are then 

 united, by delicate investments of connective tissue with fine 

 elastic fibres (a kind of perimysium), into more considerable 

 masses, iu which numerous vessels and a relatively small num- 

 ber of nerves are distributed. Chemically, the principal con- 

 stituent of smooth muscle is a nitrogenous substance similar to 

 fibrin, the so-called muscular fibrin or syntonin (Lehmaun), 

 which, from the observations that have hitherto Fi 33 Fi 34 

 been made, is distinguished from blood fibrin 

 only in this, that it is not dissolved by solution 

 of nitre, nor by carbonate of potass, but very 

 easily by dilute hydrochloric acid. 



The physiological importance of the smooth 

 muscles lies in their contractile power ; in con- 

 sequence of which they afford considerable assist- 

 ance to the functions of the different viscera. 

 The development of their elements takes place 

 simply by the elongation of rounded cells, the 

 membranes and contents uniting into a homo- 

 geneous soft substance. The nutrition of the 

 smooth muscles would seem to go on very ac- 

 tively, according to the later investigations upon 

 the fluid which bathes them, which, according 

 to Lehmann, has most generally a distinctly 

 acid reaction, and together with lactic, acetic, 

 and butyric acid, contains creatin and inosit ; 

 and the same conclusion may be deduced from 

 the frequent occurrence of physiological (in 

 the uterus) and pathological hypertrophies and 

 atrophies of them. Whether smooth muscles 

 are regenerated, or whether loss of their sub- 

 stance is replaced by a similar tissue, is un- 

 known ; on the other hand, new formations of 

 them appear to occur in uterine tumours. 



The smooth muscular fibres never form large 



Fig. 33. Muscular fibre-cell from the small intestine of man. 

 Fig. 34. Muscular fibre-cell from the fibrous investment of the spleen of the dog, 

 x350. 



