GENERAL 7 



uses and purposes which these may subserve. The child, who has just 

 learnt its letters, can hardly be expected to realize or predict the endless 

 variety or combinations of words and sentences which may be constructed 

 from the alphabet. 



When therefore we employ the knowledge obtained from other 

 sciences, it must never be forgotten that it is only by direct experimentation 

 with the living organism that we can determine whether a physiological 

 process is actually carried out by it in the way which our present knowledge 

 of Physics and Chemistry renders probable. The reasoning of one who 

 denies the possible ultimate reference of all that takes place in the organism 

 to simple chemical and physical causes is as devoid of true logic as is that 

 of the peasant who, on seeing a locomotive for the first time, argues by 

 analogy that a horse must be concealed inside ; and the same deficient 

 logic is involved in the assertion from analogy with Chemistry and Physics 

 that any final explanation of life is possible upon a purely physical and 

 chemical basis alone, for, as is well known, similar, or apparently similar, 

 final results may be attained by very different means. 



The methods employed in Physiology are in no respect different from 

 those employed in other sciences, and thus, in order to obtain a sufficiently 

 broad comprehension of the phenomena observed, and to permit the establish- 

 ment of general laws, it is essential that a comparative study of a great variety 

 of different plants should be made. The morphological relationship and the 

 common phylogenetic origin of plants and animals have long been established, 

 and it is only owing to deficient inductive reasoning that there has been so 

 long a delay in the recognition of the important fact, that there are no hard 

 and fast physiological boundaries between the two kingdoms. Essential 

 general relationships exist, not only in the metabolism of plant and animal, 

 but also in the formative power of each. The question as to how far and 

 to what extent psychical phenomena may be recognized in plants and in the 

 lower animals receives in both cases a similar answer l . All the fundamental 

 essentials of life are inherent in the undifferentiated protoplast, and even 

 the highest plant or animal is at the earliest stage of its development, as 

 a fertilized ovum, no more than a simple protoplast. No marked morpho- 

 logical differences are perceptible between the fertilized ova of different 

 plants, but nevertheless very marked inherent differences in structure and dis- 

 position must exist even at this stage, although they only become perceptible 

 in the process of development. In the protoplast a countless variety of 

 possibilities lies dormant. With progressive development, associated 

 with division of labour, individual functions become more prominent, as a 

 high degree of differentiation is attained. As a general rule, however, when 

 any modification for a special principal function takes place, the processes 



1 See Pfeffer, Die Reizbarkeit der Pflanzen, 1893, p. 30. 



