CO-ORDINATION OF SUBJECTS 37 



enzymes, and the enzymes of the stomach, for example, will not function 

 unless they are placed in an acid medium, such as the gastric juice. 

 Changes in food, or abnormalities of various kinds, may cause an excess 

 of this acid, or may prevent a sufficient quantity of the proper quality 

 being formed all such changes are chemical. 



The study of physics in its application to one's body is not so self- 

 evident and is often the bug-bear of students. Unfortunately most of 

 the textbooks on physics lay their greatest stress upon mechanical laws 

 only in their industrial applications, and fail to show how these same 

 laws apply to the human body. 



The mechanics of the living body are, however, quite similar and 

 much more important than all the industrial applications which can be 

 found. 



The three types of levers with the fulcrum in different positions is 

 the same in the body (Fig. 2) as it is in general mechanics, and a 

 knowledge of the exact points where stress and pull are applied, with a 

 consequent ability .to "figure out" where new growth structures will de- 

 velop, is of prime importance in broken, misplaced, and re-set structures, 

 if the patient is not to suffer untold agony and sorrow in future years. 



In this connection, the laws governing pulleys, the combination of 

 rolling "and sliding movements of joints, as well as the principles of 

 gravity, must be thoroughly understood ; for, it is simply and solely on 

 these principles that the various movements of the body can take place, 

 and consequently, it is only a knowledge of such principles which can in 

 turn make possible the correction of abnormalities of joints. 



The principles governing friction are applied- in the correction of 

 both internal and external injuries, while experimental physiology would 

 be impossible without a knowledge of centripetal and centrifugal forces 

 and the laws governing liquid and gaseous pressures. 



The la\vs governing liquids apply throughout the entire body in 

 great detail, for there is scarcely a spot as large as the point of a needle 

 anywhere in the body that liquid nourishment (blood or lymph) does 

 not enter. Pressure in any region causes swellings, varicose veins, 

 dropsy, and a host of other ills ; while bed-sores are nothing more or 

 less than the effect of continued pressure of blood in the same vessels 

 of the side or back on which the person lies, gravity causing the blood 

 to sink to the lowest level and be held there. 



An understanding of the difference in densities makes many physio- 

 logical experiments possible, which would otherwise result fatally to 

 the patient. A solution, if it is to be injected, must not only have the 

 proper density so as not to cause a too rapid change in the blood, but 

 the whole subject of osmosis, diffusion, and capillary attraction must be 

 understood before such an experiment can be intelligently applied. 



The place where parasites are most likely to lodge, is largely deter- 

 mined by the rapidity, direction, and pressure of the blood-stream. 



