1894.] Limits of Biological Experiments. : 847 
selections are necessary in order to maintain the highest 
development of the most desirable characters, and: a consider- 
able number of individuals will be required to make any 
marked improvement in special qualities, as all do not respond 
alike to the artificial modifying conditions of their environ- 
ment. 
There are also individuals that retain a tendency to the pre- 
potent transmission of the old race characters, notwithstand- 
ing the high development of the particular improved charac- 
ters they possess, and a pedigree, showing that all known 
ancestors have had the desired qualities, is looked upon as a 
valuable index of the dominant inherited characters. 
Even the best established breeds fail to exhibitthe uniform- 
ity in their general characteristies which prevails in wild spe- 
cies that have been subjected to the more rigorous and dis- 
eriminating processes of natural selection. The methods of 
artificial selection in the breeding of animals, are lacking in 
the inexorable consistency and comprehensiveness that char- 
acterize natural selection. The breeder of improved animals 
is unable to perceive all of their innate and acquired physio- 
logical tendencies, and his selections are made with reference 
only to the most obvious peculiarities, or qualities, and he 
overlooks and neglects many of the factors concerned in deter- 
mining the correlated relations*of the sum of their charac- 
ters. 
Feeding experiments to ascertain the relative nutritive 
value of different articles of food and the advantages of dif- 
ferent methods of feeding, or, to determine the relative merits 
of different breeds, are especially liable to mislead, from the 
complexity of the problems presented—the small number of 
facts under observation—and the practical difficulties in the 
way of tracing the obscure relations of the most significant 
factors in the phenomena under investigation, to say nothing 
of the fallacious and obsolete chemical theories of nutrition 
that are too often adopted in a popular discussion of the re- 
sults. ; 
It is not my purpose to enter upon an exhaustive discussion 
of the limits of experimental biology, but to point out some 
56 
