244 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1954 



Meanwhile, experimenters are attacking the citadel of the mind, the 

 subconscious mind at least, by the study, for example, of conditioned 

 reflexes. A clear description of one such investigation appeared in a 

 recent number of the Scientific American, in an article by Professor 

 Liddell of Cornell University on his experimental production of 

 anxiety states in sheep and goats. By the simplest physical means, 

 namely the continuous administration of slight painless electrical 

 shocks on a monotonously regular schedule, he produced long-con- 

 tinued disorders of emotional behavior. Again, anyone who has ob- 

 served the effect on human patients of drugs like desoxyamphetamine 

 has seen how high-level mental phenomena, that is to say, elaborate 

 apprehensions, conscious fears, and disorders of judgment, can be al- 

 tered for the time being by a physical agent that can only be hasten- 

 ing or retarding, somewhere in the brain, some such purely biophysical 

 action as the passage of ions across the borders of specific nerve cells. 



Rather, however, than to carry this line of argument for the ma- 

 terial nature of human thought to the length of saying outright, 

 with La Mettrie, that man is a machine and even his highest activi- 

 ties are the product of physical reactions, let us go back and look again 

 at the small living mechanism with which we started, the muscle strip 

 studied by my colleague. Simple as it seems, this little engine is ac- 

 tually much more complicated than a man-made motor. It is not made 

 of metal, but mostly of complex, unstable proteins. It is not able to 

 burn ordinary hydrocarbons like wood, coal, or oil, but only one very 

 special and elaborate substance, adenosine triphosphate. It has to 

 make this fuel for itself from sugar brought by the blood stream, step- 

 ping up the chemical structure through at least a dozen enzyme proc- 

 esses until it has built what it can burn. It is not controlled by a 

 throttle but by ion movements across a semipermeable barrier mem- 

 brane. I have by no means stated all the complexities; if we could 

 look inside this muscle when in action, w^e would see in each of its 

 microscopic cells more ions, atoms, molecules, and larger aggregates 

 going systematically about their business than all the people and auto- 

 mobiles in the city of Philadelphia. I once made a calculation that 

 one cell of an endocrine gland, the corpus liiteum, produces in one day 

 more than a thousand billion molecules of its internal secretion. 



The muscle machine is not only very complex; it is also very un- 

 stable. It runs well only within a narrow range of temperature ; 60 

 degrees centigrade will cook it; one crystal of cyanide will stop it 

 quicker than a monkey wrench in a crankcase. The protein mole- 

 cules of which it is chiefly composed are held in a precarious state 

 of teetering equilibrium by interacting tensions, like the gymnasts 

 in a human pyramid. Such is life at the level of the cell. At the 

 level of the organs — heart, lungs, liver — and at the level of the body, 

 life consists of the interaction of such complex and unstable, there- 



