All the more recent work on alkaptonuria has... strengthened the belief that the homogentisic acid excreted is derived from tyrosin, but why alkaptonuric individuals pass the benzene ring of their tyrosin unbroken and how and where the peculiar chemical change from tyrosin to homogentisic acid is brought about, remain unsolved problems.

Inborn errors of metabolism.

Nevertheless, scientific method is not the same as the scientific spirit. The scientific spirit does not rest content with applying that which is already known, but is a restless spirit, ever pressing forward towards the regions of the unknown, and endeavouring to lay under contribution for the special purpose in hand the knowledge acquired in all portions of the wide field of exact science. Lastly, it acts as a check, as well as a stimulus, sifting the value of the evidence, and rejecting that which is worthless, and restraining too eager flights of the imagination and too hasty conclusions.

Nor can it be supposed that the diversity of chemical structure and process stops at the boundary of the species, and that within that boundary, which has no real finality, rigid uniformity reigns. Such a conception is at variance with any evolutionary conception of the nature and origin of species. The existence of chemical individuality follows of necessity from that of chemical specificity, but we should expect the differences between individuals to be still more subtle and difficult of detection. Indications of their existence are seen, even in man, in the various tints of skin, hair, and eyes, and in the quantitative differences in those portions of the end-products of metabolism which are endogenous and are not affected by diet, such as recent researches have revealed in increasing numbers. Even those idiosyncrasies with regard to drugs and articles of food which are summed up in the proverbial saying that what is one man's meat is another man's poison presumably have a chemical basis.

Science is not, as so many seem to think, something apart, which has to do with telescopes, retorts, and test-tubes, and especially with nasty smells, but it is a way of searching out by observation, trial and classification; whether the phenomena investigated be the outcome of human activities, or of the more direct workings of nature's laws. Its methods admit of nothing untidy or slip-shod; its keynote is accuracy and its goal is truth.

The classic dictum that genes encode enzymes was enunciated by a physician, Archibald Garrod, who studied a patient with black urine.

What do all of these pioneers [Archibald Garrod, Oswald Avery, Peyton Rous] have in common? First, they were physicians who were trained in basic science. To them, it was not a question of physiology or medicine. To them, medicine was physiology. Second, they showed technical courage in using the most advanced scientific methods to solve medical problems.