CONTRACTILITY. 85 



more palpable change is added, that' little rows of .fat- 

 globules appear in the interior of the primitive fascicu- 

 lus, during the accumulation of which the proper con- 

 tractile substance decreases in bulk. The more fat there 

 is, the less contractile substance ; or, in other words, 

 the muscle becomes less capable of performing its func- 

 tions in proportion as the normul contents of its fibres 

 diminish. Pathological experience, therefore, also de- 

 signates as the seat of the contractile power a definite 

 substance, the occurrence of which, as especially the im- 

 portant investigations of Kolliker have taught us, is con- 

 nected with certain histological elements.. Whilst for- 

 merly many other things besides the substance of muscle, 

 as for example, certain forms of connective tissue, were 

 assumed to be contractile, lately the whole theory of 

 contractility in the human body has been withdrawn 

 within the limits of that substance, and observers have 

 succeeded in tracing back nearly all the peculiar pheno- 

 mena of motion to the existence of minute parts of a 

 really muscular nature. Thus, in the human skin there 

 lie little muscles about as large as the smallest fasciculi 

 in the parietes of the urinarybladder, bundles consisting 

 of diminutive fibre-cells, which run from the base of the 

 hair-follicles towards the surface of the skin, and, when 

 they contract, approximate the two. The result of this 

 is naturally that the skin becomes uneven, and we get 

 what is called a goose-skin. This singular phenomenon, 

 which was previously regarded as inexplicable, has been 

 simply explained by the demonstration of these purely 

 microscopical muscles, the arrectores pilorum. 



So also we now know that the greater part of the 

 muscular layers in vessels is composed of elements of 

 this kind, and that the phenomena of contraction exhi- 

 bited by the vessels must be referred solely and exclu- 

 sively to the action of muscular fibres, which are con- 



