It is of little value to look ahead and try to foresee what the next decade will bring forth in regard to the nature of the vitamines. Investigation has broadened remarkably during the past few years and now embraces the chemical field--chemical and adsorption methods, the large realm of biology, including studies in physiology and pharmacology; and recently pathology has once more been called upon to aid in the solution of the problem. Probably additional vitamines will be discovered. From time to time it has been suggested that a specific growth vitamine exists quite distinct from the three which are recognized, and recently Mellanby has suggested still another food factor--a specific "rachitic vitamine." When we reflect that the characteristic functions of the various organs--the kidneys, liver, etc.--must depend on essential differences in chemical structure, the complexity of the entire problem of unidentified factors becomes evident.[28] [28] For recent and comprehensive reviews of the vitamines the reader is referred to papers by A. B. Macallum (Trans. Royal Canadian Institute, Toronto, 1919) and by W. H. Eddy (Abstracts of Bacteriol. 1919, Vol. iii, 313.) CHAPTER IV PATHOLOGY Physicians have had a general knowledge of the pathology of scurvy for a great many years. Lind, in his "Treatise on the Scurvy," published in 1772, included a chapter on "dissections" and a postscript on "Appearances on Dissections of Scorbutic Bodies," based on a large, although indefinite, number of postmortem examinations. In the century which followed, there are to be found many reports of scurvy, especially in connection with the frequent wars, but it is surprising how little detailed pathologic information they furnish. Barlow's publication in 1883, establishing the identity of the scurvy of adults and of infants, must be regarded as the modern milestone in the study of the pathology of this disorder. This work did not contribute richly to the data of the subject, or suggest novel interpretations, but directed attention to a new source of material--the increasing number of cases of infantile scurvy--at a critical moment when the opportunity for the study of scurvy in the adult was rapidly becoming less. At the time of Barlow's exposition of the true nature of "acute rickets," scientific medicine was concentrating its interest on pathology. Tissues were being carefully studied by means of the microscope, and scurvy was subjected to this new method of investigation. As a result of intensive application of this technic, a lesion of the bones was identified and established as characteristic of scurvy. Study was focussed so exclusively on the bones, that for many years, indeed until very recently, the other organs of the body were neglected. This is true of the gross as well as of the microscopic anatomy. Protocol after protocol gives a hasty account of the appearance of the various organs, merely as