OLD AGE AND DEATH 363 



may be for the most part summed up in the conception of 

 atrophy or insufficient nutrition. This defective nutrition 

 is the prelude to an internal conflict in which the wandering 

 amoeboid cells or phagocytes, and one kind in particular, 

 which he calls macrophagous, attack the nobler tissues which 

 are no longer vigorous, which have ceased to produce pro- 

 tective substances, which have been poisoned, or which 

 have been overloaded. 



We must also notice the suggestion that the setting-in 

 of old age is due to local exhaustion of certain parts of the 

 bodily machinery with which few of us are familiar the 

 organs of internal secretion such as the thyroid gland. 

 These normally furnish to the blood some more or less 

 obscure specific substances without which vigour cannot 

 be sustained, or antitoxin substances, for instance, which 

 enable the body to resist poisons, including those of its own 

 formation. It should be remembered that even an innocent 

 substance like sugar may act as a poison. This view has 

 led to the suggestion of various modern elixirs of life 

 from injections of common salt upwards intended to re- 

 place the deficiency due to local breakdown. None of the 

 elixirs has as yet proved itself markedly efficacious, nor has 

 any good reason been given why organs of internal secretion 

 should be exhausted sooner than many other organs. 



After considering these and other suggestions as to the 

 immediate causes of old age, we feel bound to conclude 

 that in spite of their importance in furnishing descriptive 

 details of the familiar process, they do not throw much 

 light on its necessity. The law of the conservation of 

 energy makes us aware that, defiant as the organism is, 

 arrears are likely to accumulate in the activity of a com- 

 plex system, but the immortality of the Protozoa shows 

 that this dynamic bankruptcy is not inevitable. We know 

 that a carefully constructed inanimate engine may outlive 



