In Twain's "The Private History of a campaign that failed," Smith, the blacksmith's apprentice, is given the "ultimate credit" for sticking up to the war, where he was killed. 
Below is the exact quotation derived from Twain's story about Smith, the blacksmith's apprentice:
<span>"However, he had one ultimate credit to his account which some of us hadn't. He stuck to the war and was killed in battle at last."</span>
        
                    
             
        
        
        
Answer:
Myelin is an insulating layer, or sheath that forms around nerves, including those in the brain and spinal cord. It is made up of protein and fatty substances. This myelin sheath allows electrical impulses to transmit quickly and efficiently along the nerve cells.