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thing which is, comparatively speaking, accidental and pathologi- 

 cal. As I have been told that this omission may have disappointed 

 some of those who attended the lecture, I am taking the oppor- 

 tunity which has been afforded me of adding to the report of my 

 lecture a brief account of the present status of this inquiry which 

 may, in some measure, serve to supply the omission. 



It was pointed out a number of years ago, by Weismann, that 

 certain forms of living matter are, apart from accidental death, 

 in the strictest sense immortal. Thus the organisms which con- 

 sist of a single cell, such as that lowest of all animal forms, 

 Amoeba, multiply by simple division into two or more parts. 

 Each of these parts becomes a new individual, but as each of these 

 new individuals contains some proportion of the substance, or, 

 what is probably more essential, the structure of the mother cell, 

 the life of the mother cell is, in the most literal sense, continued 

 in that of its offspring. Similarly the sex cells of the higher 

 animals, such as ourselves, are the direct descendants, by a 

 repetition of such simple divisions, of the sex cells of the previous 

 generation, whose life is therefore continued in them. We are, as 

 it were, the perishable and transitory conduits of a thin uncon- 

 scious stream of immortal life. Again, it is possible to propagate 

 a tumor, by transplantation, from generation to generation of 

 short-lived animals such as mice, so that the living material which 

 is contained in such tumors to-day is, in some proportion, that 

 which was contained in the tumor of a mouse who long ago died 

 of old age. It is therefore not an inherent impossibility that 

 living matter should be immortal, yet there is perhaps no element 

 of our experience of which we feel so certain as that the sequel 

 of maturity is death, and we are therefore led to inquire whether 

 the attainment of maturity on the part of such complex and 

 highly specialized living structures as ourselves may not involve, 

 as a necessary and integral consequence, their exhaustion and 

 death. While it would perhaps be too much to say that a clear 

 and unqualified answer to this question has yet resulted from our 

 inquiry, still the results which we have obtained are such as to 

 lend very decided support to the view that decay and death are 

 not the necessary complement of growth, but that they are the 

 result of pathological processes superadded upon the normal and 

 necessary phenomena of life. 



I will endeavour briefly to describe one of the evidences upon 

 which we base this opinion. The effect of temperature upon 

 chemical reactions differs very strikingly from its effect upon the 

 majority of purely physical processes. While purely physical 

 phenomena, such as viscosity, diffusion, electrical conductivity, 

 etc., are comparatively slightly affected by a rise in temperature, 

 the velocity of a chemical reaction is very notably increased by a 

 similar agency, so that as a general rule the velocity of a 

 chemical reaction is doubled or more than doubled by a rise of 10 

 degrees Centigrade in the temperature. If, therefore, we are in 

 doubt whether the velocity of some given process is determined 

 by that of a chemical reaction or not we have only to impose 

 this test upon it, namely: — to measure the velocity in question 

 at two temperatures differing from one another by 10 degrees 

 Centigrade. If the velocity is doubled or more than doubled by 

 this rise in temperature we conclude that the underlying process 

 which determined this velocity, which "sets the pace," as it were, 

 is a chemical process. But we can do more than this ; we can 

 sort out different chemical reactions by observing the different 



