22 



Rev. S. Haughten on some Elementary [June 17, 



cyanide, in common with some other substances, was unusually great. 

 This increase of it in the urine was found to correspond with its decrease 

 in, or more frequently its disappearance from, the saliva. This circum- 

 stance goes to prove that the salt is not formed by the saliva, but is an 

 ingredient of the blood itself. 



XIV. u On some Elementary Principles in Animal Mechanics." — 

 No. II. By the Rev. Samuel Hatjghton, M.D. Dublin, 

 D.C.L. Oxon., Fellow of Trinity College, Dublin. Received 

 June 14, 1869. 



In a former communication to the Royal Society on this subject (Pro- 

 ceedings, 20th June 1867), I endeavoured to establish the two following 

 principles : — 



I. That the force of a muscle is proportional to the area of its cross 

 section. 



II. That the force of a muscle is proportional to the cross section of 

 the tendon that conveys its influence to a distant point. 



The first of these principles is true under all circumstances, but the 

 second requires to be modified somewhat in its statement. If the condi- 

 tions as to friction of the tendons that convey the action of the muscles to 

 a distant point be the same, then the force of the muscles will be propor- 

 tional to the cross sections of the tendons ; but if the tendons be sub- 

 jected to different amounts of friction, then the areas of their cross sec- 

 tions will cease to be proportional to the forces of the muscles, as represented 

 by the areas of their cross sections. 



In my former paper (No. I.), I selected, in illustration of principle II., 

 the long flexor tendons of the toes of the Rhea aud other struthious birds, 

 and showed that the cross sections of the muscles and tendons bore, ap- 

 proximately, a constant ratio to each other. Now, in the Struthionidce, the 

 conditions as to friction of the long flexor tendons of the toes are similar 

 although different in each species, and hence it was easy to prove that 

 the ratios of the cross sections of the muscles and tendons were nearly 

 constant. 



When, however, muscles and tendons, variously conditioned as to fric- 

 tion, are compared together, the constancy of the ratio of their cross sec- 

 tions disappears, and undergoes a variation depending on the friction to 

 which both muscles and tendons are exposed. 



In order to ascertain the proportion of the cross section (or force) of a 

 muscle to the cross section (or strength) of its tendon in the human 

 subject, I made the following observations on the right arm and hand of a 

 well-developed male subject in the Royal College of Surgeons in Ireland, 

 in March 1868. 



I first ascertained the specific gravities of the muscles and tendons, with 

 the following results : — 



