1892.] MICROSCOPICAL JOURNAL. 11 



contractions as well as the leap, or the motions necessary to catch a fly 

 with that movement of the tongue almost too rapid to be seen by the 

 human eye on the alert to see all the act. 



While the muscle cells have thus specialized the functions of motion 

 and can perform them with great variety and great efficiency, the other 

 protoplasmic powers of irritability, metabolism, and reproduction are 

 not lost, but only overshadowed. It would be a narrow conception of 

 muscle if we did not include these powers, though thev might from 

 their lesser prominence escape notice. The muscle cells in their sub- 

 ordination to the needs of the organism of which they form a part 

 have lost their independence even more than the ciliated cells. They 

 retain their spontaneity, they go on with their action after the body is 

 dead. They are not set at work and stopped from work by orders 

 from higher powers. The muscle cells, on the other hand, have lost 

 this spontaneitv and do not work except under orders from the nervous 

 system. But thev have the power of irritability, so that when they are 

 excited by the nerves they at once contract. They are all kept really 

 in a state of tonic (constant) slight contraction by constant impulses 

 from the nerves, and can be thence either contracted more or relaxed. 

 It is their very perfect irritability which makes the cells thus controlla- 

 ble. We can easily appreciate the case of tissues composed of cells, 

 some slightly, others strongly irritable^ by comparing such a tissue with 

 a company of soldiers. If all were not stirred to instant and simulta- 

 neous action by one word of command the company would be totally 

 worthless, and the value of the company depends on the degree to 

 which all respond as one man. It is the old maxim of strength in 

 unity. The irritability of the cell underlies the possibility of so stim- 

 ulating the hundreds of cells in a muscle like the biceps as to make it 

 perform with great precision. Not only irritability but metabolism is 

 also active in each cell and under its control. Oxygen and food are con- 

 stantly going into a muscle ; cai-bonic acid and nitrogenous waste pro- 

 ducts as constantly coming out. More go in and out when it is at 

 work than at other times. If food does not go in, the muscular cells 

 gradually waste away. Sometimes the protoplasm of a muscle cell is 

 replaced with fat and the cell ceases to be capable of contraction. 

 These and many other facts go to show that chemical changes take 

 place in the muscle, and these not at random, but under very exact 

 control. The oxygen combined with portions of the muscle substance 

 produces simpler compounds, and force is freed and used in the con- 

 traction or heat is produced, or both. The muscle cell does not, like 

 amceba, engulph its food solid, but, after the manner of yeast or the 

 inoulds or gregarina, it receives the already digested food by dialysis 

 through the wall ; but it must have food and oxygen. A mistake in 

 regard to the chemical substance it forms is fatal to the cell, as in fatty 

 degeneration, which is such a case. If these views are correct, and 

 they are in the main the present views of biologists the world around, 

 we are not wrong if we assert that the motions of the frog are all due 

 to the specialization in different directions of the fundamental proto- 

 plasmic power of motion, notwithstanding the very diverse kinds of 

 motion and the many quite different structures by which these motions 

 are produced. 



[To be coiiti?iued.'\ 



