Jeffries.] 
46 
[May 7, 
ism is gaining ground ; though, as a rule, the cases brought for- 
ward presuppose an idea of heredity. 
What is needed if physical causes are to be accredited with a 
material part in the development of organisms is, first, proof that 
outside physical changes directly change an organism ; second, 
that the changes are hereditary. That changes of condition may 
produce change in an organism is known by direct evidence. 
Schmankewitsch has shown that the crustacean Artemia varies 
greatly, as it is grown in fresh or salt water. But is the change 
hereditary ? here two stumbling blocks come in the way : the lack 
of time in the salt water and the fact that we cannot assume the 
fresh water to be without effect. If the physical conditions of the 
presence of certain salts force growth in one way, why should not 
their absence necessitate a change obverse in nature? In this case 
we should expect the change to be slow in either direction accord- 
ing to the amount of heredity attained under the previous condi- 
tions which should vary according to the time elapsed under the 
condition. Thus, individuals, the progenitors of which had been 
in salt water for ten generations might be expected to change back 
more quickly than those which represented a hundred generations 
in the saline mixture. So far as the writer knows, it is only known 
that the change in either direction requires several generations. 
Another set of changes occur with change of climate, which seem 
fairly attributable to physical causes and appear to be hereditary. 
The people of mountainous countries are as a rule large, strong 
men with great lung capacity, and their children born in the low- 
lands certainly hand down these peculiarities for some time. This 
can easily be explained by assuming that the strains with an he- 
reditary tendency to these features have been preserved by selec- 
tion. There are, however, objections to this assumption, since it 
is not by any means the large men that make the best climbers. 
Neither are the best guides in Switzerland of this type, nor are the 
best climbers among the tourists to be found among them. This 
is easily explained by the great amount of lifting to be done and 
the law by which the weight increases with the cube and the mus- 
cular strength only with the square. It is well recognized that 
light men of medium stature have a material advantage as opposed 
to large men when leg work is to be done. 
Another fact which points to the change being due to physical 
causes is that the same class of change occurs in the first individual 
