1894,] The Scope of Modern Physiology. 477 
functions in another genus does not necessarily indicate the 
presence of the same secretory functions. Nor will the line of 
functional descent of a part necessarily coincide with the line 
of morphological descent of the organism. A natural system 
of classification is based and, justly so, on morphological con- 
siderations. In thus tracing out the genetic relationships of 
function, lie the attractiveness and the utility of the compara- 
tive method in physiology. And I venture to assert that, if 
all investigators would bear in mind the fact of an evolution 
of function, surprising advances would result in our knowledge 
of the working of adult organs. i 
What is it that makes an individual physiologically what 
he is? There are two agents—heredity and the environment. 
As to heredity, the active discussion now going on around 
Weismann as a centre, serves to show what a vast amount we 
do not know, on both the morphological and the physiological 
sides as regards the general phenomena of heredity and the 
nature and behaviour of the hereditary substance. No one 
recognizes this more fully than Weismann himself. He con- 
fesses that his own theory is far from complete; that its im- 
portance consists primarily in its suggestiveness; that the real 
solution of the problem lies in the future, and that facts are 
greatly needed. In this connection I may refer to the value of 
the work of Nussbaum, Gruber, Balbiani, Hofer, Korschelt, 
Verworn and others on the physiological relations of the 
nucleus and cytoplasm. : 
The mutual relations of the environment and the individual 
are almost as unknown as when Darwin first demonstrated 
their importance. In a few special lines they have been in- 
: vestigated. In his earthworm studies Darwin himself set an 
as eminent example. The fact of the modification of the viru- 
. lence of pathogenic bacteria by their treatment during growth 
1s well known. Interesting results have been obtained re- 
_ garding the action of salt-water on fresh-water animals, and 
vice versa ; the action of salts on starch production in plants; 
the effect of depriving animals of apparently important salts, 
_& 9., fowls of carbonate of lime, and crabs of calcium chloride. 
Maupa ll-known studies on the influence of temperature on 
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