36 



General Biology 



physical side. Everyone knows that food is composed of chemical sub- 

 stances which, after being taken into the body, pass through many 

 chemical changes while being converted into new blood to keep life 

 going. The student, however, probably does not know that Louis 

 Pasteur, the Father of Bacteriology, was a chemist, and that the whole 

 modern conception of medicine is based on the bacteriological findings 

 he obtained while working on fermentation experiments in the chemical 

 laboratory. The knowledge he there gained was later applied by Lister, 

 who made aseptic surgery possible. 



The discovery of oxygen, by -a chemist, directly underlies practically 

 every experiment in physiology which can be performed, while the 

 great modern surgical advances are largely due to our ability to 

 anesthetize the patient. The anesthetics used are nitrous oxide, chloro- 

 form, and ether — all products of the chemical laboratory. 



Fig. 2. Diagrams to illustrate tbe different types of levers in their relations to 

 the mechanical action of muscles. 



A. Comparison between head, foot and elbow. 



B. Comparison between different actions of foot. 



Most muscles act on bones as levers. In physics there are three types of levers recognized. In 

 the first type (I) the fulcrum (F) lies between the place where power (P) is exerted on the lever 

 and the point of resistance or load (L). Levers of this kind are frequently met with in the body. 

 In A, (I) the weight of the skull tends to bend the head forward, while the force exerted by the 

 dorsal muscles of the neck serves to keep the head in position. 



In levers of the second class (II) the point on which power is exerted moves through a greater 

 distance than the point of resistance. Speed is thus sacrificed to power. Such levers are rare in 

 the body. An example is the body raised on the toes. 



In levers of the third class (III) the point on which force is exerted, moves a less distance 

 than the point of resistance, power thus being 1 sacrificed to speed. This is the most common form 

 of leverage in the body. The example A (III) is that of the elbow. Here the biceps and brachialis 

 muscles are attached only a short distance from the elbow-joint or fulcrum, while the hand is the 

 region on which force is exerted. A movement at the point P through a short distance will cause 

 L to move a great distance. 



