Febeuary 19, 1897.] 



SCIENCE. 



289 



to be. But the truth of things is after all 

 their living fulness, and some day, from a 

 more commanding point of view than was 

 possible to any one in Agassiz's generation, 

 our descendants, enriched with the spoils of 

 all our analytic investigations, will get round 

 again to that higher and simpler way of 

 looking at Nature. Meanwhile, as we look 

 back upon Agassiz, there floats up a breath 

 as of life's morning, that makes the world 

 seem young and fresh once more. May we 

 all, and especially may those younger mem- 

 bers of our association who never knew 

 him, give a grateful thought to his memory 

 as we wander through that Museum which 

 he founded, and through this University, 

 whose ideals he did so much to elevate and 

 define. 



William James. 

 Habvaed University. 



ON THE EFFECTS OF DISEASE AND SENIL- 

 ITY AS ILLUSTRATED IN THE BONES 

 AND TEETH OF MAMMALS* 



I WAS very glad to respond to the invita- 

 tion of your commitee to address you, for 

 the reason that I have been for a long time 

 interested in studying the effects of dis- 

 eased action and senility, I hold that they 

 are closely related and capable of being 

 compared in precise ways with other mor- 

 phological processes. 



Am I right in assuming that to no other or- 

 ganization is it so appropriate to present 

 the results of my investigation as to your 

 own? 



In a scientific sense the use of the words 

 ■* morbid ' and ' pathological ' cannot be sus- 

 tained, for it assumes the existence of 

 morbific principles. One might speak as 

 reasonably of the use of the words ' dirt ' or 

 ' weeds ' being warranted in treating of ex- 

 act conceptions. 



Disease tends to interfere with efiSciency 



*A lecture delivered before the Graduate Club of 

 the Biological Department of the University of Penn- 

 sylvania, December 7, 1896. 



— in whole or in part — of the organism in 

 which it is manifested. But this statement, 

 you will observe, in no way relates to eti- 

 ology. The difference between disease and 

 senilty is apparent rather than real; for 

 senility, like disease, is a condition tending 

 to inefiSciency. Many senile states resemble 

 diseased states and include calcification, 

 absorption, fatty degeneration, etc. But if 

 these processes help the organism by pre- 

 paring it for its work they cannot be called 

 perversions, since all of them are present in 

 early and confessedly normal states of the 

 economy. Calcification is a normal process, 

 whether we see it in the perpendicular plate 

 of the ethmoid bone in the young adult of 

 in the walls of blood vessels in the aged; 

 absorption is a normal process, whether it 

 is seen in the roots of the deciduous teeth 

 in the young or in the orbito-temporal sep- 

 tum of the aged; fatty degeneration is a 

 normal process, whether it takes place in 

 the mature placenta and prepares the way 

 to parturition or occurs in the form of an 

 areas senilis. But the results of these pro- 

 cesses are enormously divergent, one main- 

 taining physiological activities, the other 

 hastening to decay and death. 



Senility is of no definite period and, there- 

 fore, is without accurate limitation. The 

 postulate that ' wear and tear ' on tissues or 

 organs which cannot be replaced occur in 

 direct ratio to use is accepted. In low forms 

 of life large portions of the economy, and 

 some tissues even in the highest forms, are 

 discarded and new ones take their place. 

 Epithelial elements are constantly being 

 thrown off, and in many animals teeth are 

 lost when no longer of service and others 

 are developed to supplant them. But in 

 old age of high grade organisms we witness 

 loss, rather than gain, both in organs, like 

 the teeth and hair, and in tissues, as mus- 

 cle fibres in the capillary blood vessels. So 

 far as man is concerned, this period is, on the 

 whole, included in the time when he is no 



