More prosaic and less imaginative scientists do not see evidences of psychology in the signs of life in the protista, or ethics in the movements of a cell, but merely the effects of universal chemical and physical laws which also control lifeless inorganic matter. To these laws they trace the tropisms of simple organisms which tempt the imagination, prone as it is to anthropomorphism, into errors; such tropisms, that is to say, as their tendency to seek moderate warmth, certain rays of light and weak alkaline solutions, or to avoid acids, heat and ultra-violet rays. The little organisms probably do not obey these impulses for reasons of pleasure or pain any more than the iron filings obey the attraction of a magnet for such reasons. They do not fly to it because it gives them pleasure; the little metal leaves of an electroscope do not move apart because contact with each other displeases them. All forms of tropism, chemicotropic, thermotropic, phototropic manifestations, active and passive tropisms clearly show that minute organisms involuntarily and unresistingly respond to the influence of natural forces, just as if they were inanimate particles.
Microscopic investigations reveal many phenomena which one is tempted to consider signs of life, but which cannot be such, as they occur in connexion with inanimate matter. The Brownian movements are rhythmical molecular changes of position, not due to any mechanical impulse emanating from the surroundings, nor to a current in the fluid in which the object of investigation is immersed, but arising from the object itself, mostly very finely divided, tiny balls of mercury. A very small drop of chloroform introduced into a fluid of different density behaves exactly like a unicellular organism. It sends out pseudopods, wriggles and draws them in again. The pseudopods seem to feel and examine particles of matter with which they come in contact, and then either to withdraw quickly from them or to surround and incorporate them in the drop. This is deceptively similar to the behaviour of a living cell absorbing food, though there can be no question of this in the case of the drop of chloroform. In the latter it is merely a question of the effects of surface tension, that is, of the normal behaviour of matter in accordance with the laws governing the forces of nature, the investigation of which lies in the domain of chemistry and physics.