MUSCLE 545 



canal. These actions are very different, but the muscles 

 that carry them out are at bottom very similar. And it 

 cannot be doubted that the functional differences are due 

 entirely, or almost entirely, to differences of anatomical 

 connection, on the one hand with bones and tendons, on 

 the other with the nerve-cells of the spinal cord and brain. 

 The common properties in which all the skeletal muscles 

 agree are the subject-matter of the general physiology of 

 striated muscle. 



The cardiac muscle differs more, both in structure and in 

 function, from the skeletal muscles than these do among 

 themselves ; the smooth muscle of the intestines and blood- 

 vessels still more. But every muscular fibre, striped or 

 unstriped, resembles every other muscular fibre more than 

 it does a nerve-fibre or a gland-cell or an epithelial scale. 

 The properties common to all muscle make up the general 

 physiology of muscular tissue. 



A nerve-fibre is at first sight very different from a muscular 

 fibre. It has diverged more widely from the primitive type 

 of undifferentiated protoplasm. It has lost the power of 

 contraction, or contractility, but it retains, in common with 

 the muscle-fibre, susceptibility to stimulation, or excitability, 

 the capacity for growth, and to a limited extent the capacity 

 for reproduction. This inheritance of primitive properties, 

 retained alike by both tissues, is the basis of the general 

 physiology of muscle and nerve. 



The electrical organ of the Torpedo or the Malapterurus 

 is intermediate in some respects between muscle and nerve, 

 and has properties common to both. In the gland-cell the 

 chemical powers of native protoplasm have been specialized 

 aud developed. Contractility has been, in general, entirely 

 lost ; but excitability remains. The idea that certain common 

 endowments find expression in the action of muscle, nerve, 

 electrical organ, gland, etc., in the midst of all their apparent 

 differences is the basis of the general physiology of the 

 excitable tissues. 



Amoeboid movement is the most primitive, the least elabo- 

 rated form of contraction. An amoeba may be seen under 

 the microscope to send out pseudopodia, or processes, of its 



35 



