28 THE EYE IN EVOLUTION 



were held to be pre-human in the sense that they were the evolutionary 

 forerunners of the mental attributes of man.^ Emotions were thus 

 attributed to the lowest animals so that their conduct could be equated 

 to that of man who was their descendant. The rationalization of 

 zoology thus lagged behind that of botany, the progress of which seems 

 to have been unnoticed by those engaged in the study of animal life, 

 possibly because the temptation to endow plants with anthropomorphic 

 attributes was less compelling. 



In extenuation of the general acceptance of what would be considered a 

 shallow philosophy today, it must be remembered that the doctrine of " animal 

 spirits " was of extreme antiquity ^; as a basis of his philosophy man required 

 the concept of an incorporeal essence to give meaning even to corporeal objects, 

 a need still felt by such philosophers as Descartes (1650-64) and such scientists 

 as Willis (1670) and Boerhaave (1708) ; and it was not until almost the middle 

 of the 19th century that the physical discoveries of Galvani (1791), the anatomist 

 of Bologna, and Volta (1796-1800), the physicist of Pavia, were applied to the 

 reactions of living creatures by the two great founders of modern physiology, 

 Johannes Miiller (1834) and du Bois-Reymond (1843-49), who laboriously began 

 to build ujD a physiological doctrine on a physical basis. Almost half a century 

 was to pass, however, before these new concepts, already accepted by botanists 

 and for long part of physiological teaching, were applied to the problems of the 

 orientation of animals by light and other stimuli. The early experimenters in 

 this field from Paul Bert (1869) to Graber (1883-84) interpreted these reactions 

 in anthropomorphic terms : animals sought or avoided light because it was 

 " agreeable " or " disagreeable " ; indeed, the experimental studies of Engel- 

 mann (1879-82) and Verworn (1889) were the first in which attempts were 

 made to place a physiological interpretation upon these responses, attempts 

 which rapidly fructified so that the doctrine soon became generally accepted by 

 zoologists and physiologists.^ 



At the beginning of this period of activity and reorientation, a 

 prophet arose in the person of the German biologist, jacques loeb 

 (1859-1924) (Fig. 11). Loeb's life-work was a study of the differentia- 

 tion between the animate and the inanimate and his thesis the identity 

 of the two, for to him all living things were chemical and mechanical 



1 Darwin (1872), Lubbock (1881-89) in England ; Paul Bert (1869), Plateau (1886), 

 Binet (1894) in France ; Graber (1883-84) in Germany ; Romanes (1883) in America ; 

 and others. 



^ This belief permeated the whole of ancient thought and mythology. Even 

 although the philosophy of the Ionian Greeks became more impersonal than the bronze- 

 age cosmologies, Thales of Miletus, c 625-545 B.C., the first of the .Greek natural 

 philosophers, ascribed a soul to the lodestone because it could move a piece of iron, a 

 view generalized by Anaxagoras, c 488-428 B.C., who ascribed all motions of material 

 or living things to the operation of a mind or a soul. Erasistratus of Chios, ^. c 300-260 

 B.C., believed that the inspired air was transferred into vital spirit in the heart, to be 

 relayed as such all over the body by the arteries ; the small amount reaching the brain 

 was again transformed into animal spirit {animus, a soul) which was distributed by 

 the nerves ami was responsible for sensitivity and movement. The same philosophy 

 was further elaboiated by Galen, a.d. c 130-200, and for centuries was an accepted doc- 

 trine. 



3 Loeb (^ 1913), Jennings (1904^-6), Mast (1906-38), Bohn (1909), Patten 



(1919), and oti 



