To a physiologist, who requires assistance _from all branches of science_, Chemistry must always be an interesting study. When we lay aside all speculations as to what is the abstract nature of Life, and study that which is the proper object of philosophy—that to which it seems the faculties of man are limited—namely, the _laws_ in obedience to which the phenomena in nature occur; and apply the knowledge thus obtained to the occurrences which take place in the human body; we soon discover that, whatever the abstraction "Life" may be, we live proximately, in virtue of certain changes in various forms of matter; as food, air, the various constituents of our bodies, &c.; and that these consist of multiplied separations and rearrangements of their respective elements, which it is the special province of Chemistry to examine. If we investigate the changes of the living, or the structure of the dead, with these objects,—we shall be in no danger of perverting Chemistry to purposes to which it is inapplicable. When, however, we proceed a step further, and seek to give a _chemical expression_ to various uses and relations of different parts of the body, the greatest caution is required. In the first place, in a machinery which is a practical application of a great _many_ sciences, it is to the last degree improbable that they can be expressed by any _one_. Again, to estimate the true meaning—the physiological interpretation of many changes which might be in their proximate sense chemical,—a greater familiarity with the phenomena of _disease_ is necessary than _usually_ falls within the inquiries of _the most scientific chemist_. To a person acquainted only with the ordinary phenomena of health, or who is not even something also of a philosophical pathologist, Chemistry is for ever suggesting tempting analogies, which are constantly tending to mislead him to conclusions on insufficient data; and to examine and rest too much on the _chemical_ facts deducible from one or other function, without sufficiently attending to the _physiological_ relations of that function with _all_ others. In fact, for want of due caution, or it may be of a sufficient range of information, the assistance which Chemistry has hitherto rendered to Physiology has been attended with so many assumptions, that it is extremely difficult to say on which side the balance lies—of advantage or error. We are aware that at this moment there is a contrary feeling—a kind of _furore_ for _chemical_ solutions of _physiological_ phenomena. We believe the caution we venture on suggesting was never more necessary.