188 J: LIONEL TAVLIER [SEPTEMBER 
is due to a structural difference existing in the protoplasm itself, that 
the assinilative power of an organism depends not on its environment 
but upon its structure, and that these structural peculiarities are never 
modifiable, although they may be adapted through elimination of 
unfit and less fit, and subsequent reproduction among the surviving 
favoured organisms, and repetition of this process until a better and 
better adapted organism is produced, we have an explanation which 
satisfactorily accounts for both the constancy and the variability of 
the many forms of plant life. 
Again, the constancy of all low forms of lfe under varying 
conditions is often remarkable. In view of the fact that these 
unicellular organisms are not easy to keep under constant observa- 
tion, that their reproductive power is often enormous, and that it 
is at present very difficult if not impossible to place them under 
test conditions to prove whether or no they are capable of being 
directly modified by changes in temperature, food, etc., it is worthy of 
note that the few recorded experiments have taken years and not 
months or weeks to induce any change in the organism, and this 
suggests elimination rather than direct modification as the main if not 
sole agent. 
The science of bacteriology is surely strong presumptive evidence 
that no very rapid modification of form and habits is affected by 
altered conditions in these low forms of life; the constancy of the 
characters of diseases known to be produced by these forms of micro- 
organisms, and the fact that the bacteriologist can frequently tell by 
the form and behaviour of the bacillus, micrococcus, ete., what disease 
it will induce, and this in spite of the immense capabilities for 
modification under changed conditions, etc., that its habits afford, 
are all arguments against direct climatic accommodation. 
Another point which appears to me to throw very considerable 
light on the subject is the behaviour that all organisms, as far as 
I know, without exception, exhibit towards their environment. 
Local conditions of light, heat, food-supply, do not appear to modify 
organisms in a certain definite manner as one would expect were 
direct climatic accommodation possible; on the contrary, the action of 
every organism to its environment, from the lowest to the highest, 
appears to be selective, the response of certain internal activities to 
outside conditions. Recent observations made on the phagocytes of 
the blood show that the determination of their movements is partly 
chemical, that they move away from some and towards other products ; 
their action is selective. Plants lving on the same soil do not make 
use of the same material, and it is perfectly extraordinary what 
minute quantities of a substance can be utilized if it be needed by the 
organism. Iodine and its selection from sea-water by some forms 
of sea-weed is a case in point. Precisely similar results occur in the 
animal kingdom. The same choice of food is manifested in different 
