That the external features as well as the chronic diseases of human beings are controlled by some common factor has long been suspected. Inquiries into morbid phenomena with a hereditary trend yielded information that has paved the way for the internal secretion theory. It has long been known that certain diseases effect only certain individuals of a definite constitution. Apoplexy, diabetes, arteriosclerosis, Bright's disease, are met with almost exclusively in what the older clinicians talked about as the apopleptic type. On the other hand, they said, anemias, tuberculosis, hemophilias, scrofulas occurred more among the lymphatic type. But they had no idea whatever of the true functional basis of the two different types. The truth as we of today view it is that these two types represent different textures of human beings, fabricated of different internal secretions. They are really two different breeds of the species Homo Sapiens. The materials being different, the color and feel of them is different, and the resistance to wear and tear is different. ENDOCRINE ANALYSIS The modes of classification glimpsed at are certainly exceedingly broad and sweeping. It is well enough to establish types and classes. But beneath them are sheltered the infinite possibilities of permutations and combinations, which explain the countless variety and complexity of form and function. Every individual born among the vertebrates, for example, must have a certain definite amount and percentage of pituitary gland, anterior and posterior, pineal, thyroid, parathyroid, thymus, adrenal, pancreas, interstitial and so on. Now if, to state it in terms of percentages, for the sake of argument, the pituitary is 25, the pineal 10, the thyroid 36, the parathyroids 15, the thymus 29, the adrenals 60, the pancreas 49, the interstitials 72 (the gland when acting maximally to be graded as 100), we see at once how different such an individual must be from one who has, say, pituitary 84, pineal 39, thyroid 26, parathyroid 42, adrenals 96, pancreas 22 and interstitials 89. One obtains at once from the contrasts of such figures some idea of the possibilities. As each point plus or minus must count to produce some difference in the individual, the results are manifest. Varying within the numerical limits imposed by genus, species, variety and family (which limits are probably responsible for the persistence of the particular genus, species, variety, or family) the individual becomes an individual because of the relative values of the percentages in his blood and tissues of these different internal secretions. We thus begin to gain an insight into the patterns according to which men, women and animals are woven.