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he student。 In the name of the Faculty I welcome you； Gentlemen of the Medical Class； new…born babes of science； or lustier nurslings； to this morning of your medical life； and to the arms and the bosom of this ancient University。 Fourteen years ago I stood in this place for the first time to address those who occupied these benches。 As I recall these past seasons of our joint labors； I feel that they have been on the whole prosperous； and not undeserving of their prosperity。
For it has been my privilege to be associated with a body of true and faithful workers； I cannot praise them freely to their faces； or I should be proud to discourse of the harmonious diligence and the noble spirit in which they have toiled together； not merely to teach their several branches； but to elevate the whole standard of teaching。
I may speak with less restraint of those gentlemen who have aided me in the most laborious part of my daily duties； the Demonstrators； to whom the successive classes have owed so much of their instruction。 They rise before me； the dead and the living； in the midst of the most grateful recollections。 The fair； manly face and stately figure of my friend； Dr。 Samuel Parkman； himself fit for the highest offices of teaching； yet willing to be my faithful assistant in the time of need； come back to me with the long sigh of regret for his early loss to our earthly companionship。 Every year I speak the eulogy of Dr。 Ainsworth's patient toil as I show his elaborate preparations： When I take down my 〃American Cyclopaedia〃 and borrow instruction from the learned articles of Dr。 Kneeland； I cease to regret that his indefatigable and intelligent industry was turned into a broader channel。 And what can I say too cordial of my long associated companion and friend； Dr。 Hodges； whose admirable skill； working through the swiftest and surest fingers that ever held a scalpel among us； has delighted class after class； and filled our Museum with monuments which will convey his name to unborn generations？
This day belongs； however； not to myself and my recollections； but to all of us who teach and all of you who listen； whether experts in our specialties or aliens to their mysteries； or timid neophytes just entering the portals of the hall of science。 Look in with me； then； while I attempt to throw some rays into its interior； which shall illuminate a few of its pillars and cornices； and show at the same time how many niches and alcoves remain in darkness。
SCIENCE is the topography of ignorance。 From a few elevated points we triangulate vast spaces； inclosing infinite unknown details。 We cast the lead； and draw up a little sand from abysses we may never reach with our dredges。
The best part of our knowledge is that which teaches us where knowledge leaves off and ignorance begins。 Nothing more clearly separates a vulgar from a superior mind； than the confusion in the first between the little that it truly knows； on the one hand； and what it half knows and what it thinks it knows on the other。
That which is true of every subject is especially true of the branch of knowledge which deals with living beings。 Their existence is a perpetual death and reanimation。 Their identity is only an idea； for we put off our bodies many times during our lives； and dress in new suits of bones and muscles。
〃Thou art not thyself； For thou exist'st on many a thousand grains That issue out of dust。〃
If it is true that we understand ourselves but imperfectly in health； this truth is more signally manifested in disease； where natural actions imperfectly understood； disturbed in an obscure way by half… seen causes； are creeping and winding along in the dark toward their destined issue； sometimes using our remedies as safe stepping…stones； occasionally； it may be； stumbling over them as obstacles。
I propose in this lecture to show you some points of contact between our ignorance and our knowledge in several of the branches upon the study of which you are entering。 I may teach you a very little directly； but I hope much more from the trains of thought I shall suggest。 Do not expect too much ground to be covered in this rapid survey。 Our task is only that of sending out a few pickets under the starry flag of science to the edge of that dark domain where the ensigns of the obstinate rebel； Ignorance； are flying undisputed。 We are not making a reconnoissance in force； still less advancing with the main column。 But here are a few roads along which we have to march together； and we wish to see clearly how far our lines extend； and where the enemy's outposts begin。
Before touching the branches of knowledge that deal with organization and vital functions； let us glance at that science which meets you at the threshold of your study； and prepares you in some measure to deal with the more complex problems of the living laboratory。
CHEMISTRY。 includes the art of separating and combining the elements of matter； and the study of the changes produced by these operations。 We can hardly say too much of what it has contributed to our knowledge of the universe and our power of dealing with its materials。 It has given us a catalogue raisonne of the substances found upon our planet； and shown how everything living and dead is put together from them。 It is accomplishing wonders before us every day； such as Arabian story…tellers used to string together in their fables。 It spreads the； sensitive film on the artificial retina which looks upon us through the optician's lens for a few seconds； and fixes an image that will outlive its original。 It questions the light of the sun； and detects the vaporized metals floating around the great luminary；iron； sodium； lithium； and the rest；as if the chemist of our remote planet could fill his bell…glasses from its fiery atmosphere。 It lends the power which flashes our messages in thrills that leave the lazy chariot of day behind them。 It seals up a few dark grains in iron vases； and lo！ at the touch of a single spark； rises in smoke and flame a mighty Afrit with a voice like thunder and an arm that shatters like an earthquake。 The dreams of Oriental fancy have become the sober facts of our every…day life； and the chemist is the magician to whom we owe them。
To return to the colder scientific aspect of chemistry。 It has shown us how bodies stand affected to each other through an almost boundless range of combinations。 It has given us a most ingenious theory to account for certain fixed relations in these combinations。 It has successfully eliminated a great number of proximate compounds； more or less stable； from organic structures。 It has invented others which form the basis of long series of well…known composite substances。 In fact； we are perhaps becoming overburdened with our list of proximate principles； demonstrated and hypothetical。
How much nearer have we come to the secret of force than Lully and Geber and the whole crew of juggling alchemists？ We have learned a great deal about the how； what have we learned about the why？
Why does iron rust； while gold remains untarnished； and gold amalgamate； while iron refuses the alliance of mercury？
The alchemist