ANATOMY AND HISTOLOGY OF AGING SKIN 303 dermis of young and old individuals than when it was not so separated. Of course, it must be remarked that this process itself is one which may make a difference in the appearance of the epidermis, that is, the separation of it from the dermis. Thuringer and Cooper (25) reported on the study of abdominal skin removed at surgical operations from 34 persons ranging from youth up to very advanced age. They studied both serial sections and total mounts. They• found that there was an atrophy and loss of the fete pegs in old age. They also made studies on the number of cells which were dividing in the skin of people of different ages. They found that there were actually more cells dividing in old age than in the younger persons. Hill and Montgom- ery (14) also had described such atrophy of the fete pegs. There is often an increase in number of pigment spots in the epidermis in senile individuals. Two of the studies which we have mentioned ear- lier may throw some light on this subject in that the findings of Hill and Montgomery (14) on skin which generally is protected by clothing indi- cated that there was no increase in pigmentation in such skin while the finding of Ejiri (9) on skin which is generally exposed did show an increase in pigmentation. Again, we may be dealing with extrinsic factors entirely or with extrinsic factors imposed upon the inner physiological change in the body. We come now to the appendages of the skin. Graying of hair due to loss of pigment is definitely associated with advancing age but also the color of hair which has not lost its pigment changes with age. Thus the hair of young individuals is lighter in color than that of older ones and the incidence of darker tones is greater with advancing age. In white hair we find an absence of pigment in and around the cells of the cortex but we do not understand yet what causes this loss of pigment. White hairs may or may not be greater in diameter than their pigmented neighbors. In regard to the glands of the skin there are some statements in the litera- ture that both the oil or sebaceous glands and the sudoriferous glands become atrophic and actually decreased in number in senile skin but there is very little experimental work to show this to be the case in fact, in some cases sebaceous glands seem to be larger in old age, as on the forehead. Actually, we have no clear-cut information on age changes of the sweat glands. Some workers have tried to correlate functional changes of the skin, such as the amount of secretion appearing on its surface, with the gross appearance of the skin. Thus, Kvorning and Kirk (17) tried to make a correlation between the clinical estimation of the condition of the skin and certain skin secretion tests. They found actually a good correlation between the quantity of lipid secreted on the forehead and the appearance of the skin. In the female subjects a correlation was also found between the lipid secretion and the greasiness, thickness and turgot of the skin.

304 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS There was not any correlation between the degree of wrinkling or furrow- ing and the amount of secretion. The positive correlation, then, was between the presence of distinct and enlarged skin pores and the presence of a higher amount of lipid secretion. There was also a good degree of correlation between skin thickness and lipid secretion in the women but not in the men. We are interested in this paper primarily in the normal anatomy and his- tology of skin. A nnmber of recent articles, besides attempting to sum- marize the normal characteristics, describe the disease conditions most common for the aging skin (30, 16, 24, 21). PERSONAL RESEARCH ON AGING OF THE SKIN In planning our investigations on age changes in the skin it seemed wise to try to use both animal and human material. Certainly there is such a very large amount of intrinsic interest that attaches itself to the study of human tissues that we felt determined to make such an investigative study. On the other hand, there are so many factors involved in the variations in different tissues of human beings such as pathological conditions, race and other things that it seemed very wise to attempt also to study animal skin and particularly skin of pedigreed animals. We therefore made an arrange- ment with the Wistar Institute whereby it was possible to obtain specimens of skin from different parts of the body of the pedigreed Wistar Institute rats. These include specimens from the back in the region between the scapulae, from the abdomen, near the mid-line, from the ear and from the sole of the forepaw. Our human material consists now of almost 200 individuals, minute samples having been taken from various regions of the body at the time of surgical operation. The skin is so stretchable and so easily regenerated that the taking of such minute specimens does not inconvenience the patient in any way. In this manner it has been pos- sible to obtain representative sections of skin from people of many different ages and skin which is essentially normal in all respects. Careful records are kept of the type of surgical operation involved and, of course, of the general record of the patient so that the material on these individuals is always accessible through our hospital files. However, in general, the operations are such that the condition of the patient is essentially normal except for the particular pathology such as appendicitis, abdominal preg- nancy or some other such condition in which it is not expected that the con- dition of the skin will be other than normal. We now have made three individual studies on the skin of the Wistar Institute rats. The first was concerned with the general characteristics of the dermis and the epidermis and the second with the cell types in the epidermis of the back while the third concerns the cell types at different ages in the epidermis of the abdo- men.