INTRODUCTION. 



DISEASE may be defined as being any condition of the organism which limits life in 

 either its powers, enjoyments, or duration. This, we admit, is not a strictly 

 scientific definition, but it is, we believe, as good a one as can be given in the present 

 state of our knowledge. It is obvious that we cannot give a strictly accurate defi- 

 nition of disease until we possess a satisfactoiy definition of " health," and this we 

 are not likely to arrive at until we can express in words the idea that we entertain 

 of the still more fundamental fact of " life." 



Fortunately for us it is possible to study the principles of health and disease, 

 without being called upon to define what we mean by these terms. It is not always 

 easy to express our meaning in a few set words, nor is it necessary that we should do 

 so. We all understand that in health we recognise the natural or standard condition 

 of the living body. We all know that it implies freedom from pain and sickness, and 

 freedom from all those changes in the natural fabric of the body that endanger life or 

 impede the easy, regular, and effectual exercise of the vital functions. Health does 

 not signify any fixed and immutable condition of the body, for the standard varies in 

 different persons according to age, sex, and original constitution, and even in the same 

 person from week to week, and day to day. Health does not necessarily imply the 

 integrity of all the bodily organs, for a man may be perfectly healthy who has lost 

 an eye, or even an arm or a leg. If we can only form a clear conception of what 

 we mean by health we shall have no difficulty in understanding what is meant by 

 disease, for disease, as we have already seen, is some deviation from the normal 

 standard of health. By disease we understand some uneasy or unnatural sensation 

 which is manifest to the patient, some embarrassment of function which he or his 

 friends may perceive, or some unsafe though hidden condition of which he may be 

 quite unconscious. 



It should be borne in mind that by disease we mean the sum total of certain 

 morbid changes that take place within the body. The mistake is often made of 

 supposing that disease is a something which has a distinct entity, that it is something 

 th.it is taken into the body, and may be cast out again by appropriate remedies. 

 You often hear patients, and even doctors, talk of " driving the disease off through 

 the kidneys," or " sweating it out of him." Many people seem to regard disease 

 as being something which has distinct physical properties, something that can be felt 

 and seen. It is common enough to hear people say that " he threw the disease off" 

 his stomach, just for all the world like a lump of currant jelly," or for them to use 

 some expression showing equally conclusively that they regard disease as having a 

 distinct entity. 



As has been very truly said, disease under all circumstances and to all degrees, is 



