234 PHYSIOLOGY AT THE FARM. 



peatedly unite with each other in the form of a plexus, and 

 that is most commonly confined to a small part of the length 

 or muscular division to which it belongs. It is doubtful if the 

 nerve-fibres penetrate the sarcolemma. 



The solution obtained from lean beef by means of cold water 

 gives the soluble substances present in muscle. These consist 

 of albumen, the soluble salts of the blood, of the crystallisable 

 animal principles named kreatine and inosine, of phosphoric 

 acid, and at least three organic acids viz., the lactic, the ino- 

 sinic, and the butyric. Possibly also acetic and formic acids 

 are present in small quantity. The colour of the solution is 

 due to the red colouring matter of the blood. The salts con- 

 sist chiefly of phosphate of potassa, phosphate of magnesia, 

 and a small quantity of chloride of sodium and of phosphate 

 of lime.* 



A muscle when in action is shortened ; at the same time it 

 swells in the middle, and becomes firm and rigid to the feel. 

 This state after a short time is succeeded by relaxation. No 

 change of volume occurs during the action of a muscle. The 

 stimuli to action are mechanical irritation, chemical stimuli, 

 electrical stimuli, sudden heat or cold ; lastly, mental stimuli 

 and organic stimuli. 



A muscle does not contract throughout at once : it appears 

 that numerous contractions and relaxations take place suc- 

 cessively in different parts during what seems to be its con- 

 traction. A considerable waste of organic substance is sus- 

 tained during the action of a muscle. 



Nervous Texture. The nerve or ganglionic cells were already 

 referred to (p. 216). The nervous system consists of a central 

 part, or rather of a series of connected central organs, called the 

 cerebro-spinal axis or cerebro-spinal centre, and of the nerves in 

 the form of cords connected by one extremity with the cerebro- 



* Miller, 'Elements of Chemistry,' part iii. p. 782. 



