Apkil 4, 1919] 



SCIENCE 



321 



not needed here, yet I do want to point out 

 that these tests show in a somewhat precise 

 way a fact that can hardly have failed to 

 strike us all, namely, that our associates stop 

 growing mentally at quite different ages, some 

 continuing to grow long after others have 

 reached their limit. 



When Cato learned Greek at eighty years 

 it indicated more than that the farm was 

 doing well and he had time to spare. It 

 indicated a capacity for new interests and a 

 mental retentiveness which are among the 

 virtues of the youthful mind. 



These are endowments which we would all 

 desire but which are unevenly possessed. 

 However, in any discussion which involves 

 the problem of nature versus nurture, it can 

 always be pointed out that whatsoever nature 

 has or has not done, there still remains the 

 pyossibility of modifying nurture — or the en- 

 vironment — and these possible modifications 

 are worth attention. 



Observation shows us that the differences 

 between men are small, but that, small as 

 they may be, they amount to a great deal. 

 Slight improvement is worth a struggle and 

 repays the effort. I am commending to you 

 therefore the effort to keep growing mentally. 



A remarkable example is that of Helmholtz. 



Helmholtz began as a physician — a very 

 mediocre practitioner they say — but under the 

 inspiration of Johannes Miiller he became in- 

 terested in physiology. This branch he fol- 

 lowed by the study of the eye and ear, leading 

 to his great works on physiological optics and 

 sensations of tone — by the way devising that 

 important instrument the ophthalmoscope. 

 But the physiology of the sense organs called 

 for physics. So well did he follow this lead 

 that he became one of the first physicists, and 

 linked his name with the doctrine of the con- 

 servation of energy. Still going forward he 

 developed his mathematics and became em- 

 inent in that field also. Here is a steady 

 growth through a long life. A great intellec- 

 tual engine at his command was applied to 

 field after field in succession, and always witli 

 a resulting advance in knowledge. 



Such men set the pace and these pace- 



makers are the most helpful members of our 

 race, for while those who have stopped grow- 

 ing have but a single response, " It can't be 

 done," the pace-makers do it. 



Xaturally you ask what is the formula, 

 how is it accomplished? Let me reply by a 

 question: What do you think about when you 

 are not working? For most of us that period 

 represents the larger part of life, and it does 

 make a difference what we do with this great 

 fraction, so I will leave the implications of 

 my question without elaboration, but ask you 

 to meditate upon it. 



There is however a further matter which 

 lies closer at hand. Let us consider the 

 " Bohemian." I mean the individual who 

 bears this name by virtue of his behavior. He 

 is worthy of attention. He protests against 

 the restriction of conventions, sometimes in a 

 not too seemly manner, but at his best with 

 the hope of getting free from conditions which 

 hamper thought or work. We all suffer from 

 these restrictions in a mild way. By all ac- 

 counts the savage seems to be most completely 

 surrounded by taboos and conventional re- 

 straint. His is noc a happy lot. Civilized 

 man suffers less, and yet conventions stand 

 in our way. 



The necessity of getting back for dinner 

 cuts into an experiment. The idea that one 

 retires at a certain hour limits a series of ob- 

 servations. Very trifling these conditions, you 

 will say, yet breaking life up into small 

 lengths in a way which often interferes. War 

 teaches us something here that may be useful. 



In this connection I love the story of von 

 Baer. Yon Baer, the embryologist, tells how he 

 went into his laboratory when the leaves were 

 falling in the autumn and came out again 

 when the spring flowers were in bloom. That 

 was a day's work that counted, and we can 

 do well to jyonder on it Von Baer was the 

 sort of Bohemian I have in mind. 



Here I rest my case. 



The past four years have meant great things 

 for medicine. For the first time in history 

 the fighting man has had the best that med- 

 icine could give. Certain forms of practise 

 liave advanced by leaps and bounds, and you 



