1062 The American Naturalist. [December, 
. avoid the inference that there is some direct connection 
between them. Our ability to so rigidly govern the experi- 
mental conditions makes the case much stronger for these con- 
clusions, than in those cases where the variations occur spon- 
taneously. Whatever may be the true cause, or causes, that 
lead to variation among species, it cannot be denied that experi- 
ments from all classes of organic life will be valuable in add- 
ing to the store of observed facts, and thus giving us a broader 
basis upon which more accurate generalizations can be made. 
The evidence already at hand from the realm of the bacteria is 
promising enough to lead to the conviction that continued 
experimental work with reference to the problems of variation 
will be fruitful in results. 
Few problems in biology are more prominent in the discus- 
sions of to-day than those pertaining to the subject of heredity. 
Among the different phases of this subject none hold a more 
important place than the doctrine of the transmission of 
acquired characters. The difficulties of the question are 
largely increased by our inability to define exactly what is 
meant by an acquired character. Under ordinary conditions, 
it is not easy to sharply differentiate between a variation 
brought about by an inherent tendency of the organism to 
vary, and one that is impressed upon the organism from with- 
out. We have however in the phenomena of artificial immun- 
ity, whereby a susceptible animal is rendered refractory to- 
ward a specific disease germ, a favorable field for the study of 
this problem. Artificial immunity is par excellence an acquired 
characteristic, as it is a deep seated and permanent change in 
the constitution of the animal that is produced through the 
influénee of an exterior force. Several instances are on record 
that claim the transmission of acquired immunity in animals 
from the parent to the young. Chauveau found that the artifi- 
cial immunity conferred upon goats was transmitted to their 
progeny but these cases are not pertinent to the problem of the 
transmission of an acquired character, for the possibility of a 
direct transference of the immunity by means of the body 
fluids is not excluded. All cases of the so-called transmission 
of artificial immunity that are conferred upon pregnarft ani- 
d 
