While the laws Of health and disease are as firmly fixed and as immutable as the other laws of Nature, they cannot be stated as yet in positive and definite terms. Our knowledge of these complex laws is far too incomplete for us to grasp even all of the salient points, to say nothing of many of the details. In the main, however, the underlying principles Of the laws of health and disease have been disclosed and have been tested and proven by experience. The health Of the individual depends upon many factors, although all may be classified in two groups, heredity and environment. While in some instances heredity is the predominating factor, in more environ ment is the determining factor in the life of the in dividual even to the extent Of modifying the in?uence Of heredity.