ARE ACQUIRED CHARACTERS HEREDITARY? 343 
fetus. For instance, the blood of young shortly after birth may show 
a higher titer than that of the mother. Again, after two or three 
months of development the young of certain of the sensitized mothers 
have shown a rather sudden rise in titer, much above that of the 
mothers. In such cases it would seem that some mechanism in the 
young rabbit itself is constructing antibodies which supplement those 
passively derived from the mother. Possibly in the process of develop- 
ment some organ important in such reactions just came into function- 
ing. If this is true further experiments may throw some light on the 
perplexing question of the source or sources of the antibodies in an 
animal. After a few weeks, in such cases, the titer drops back again. 
In still another set of experiments we found that young from a sen- 
sitized mother, when nursed by a normal untreated mother, retained a 
fairly high titer for several months and even showed the rise of titer 
mentioned. On the other hand, young of an untreated mother when 
nursed by a sensitized mother acquired a fairly high titer from the 
milk of the foster mother but lost it rapidly after weaning time. Thus 
there are evidently constitutional factors operative in the young which 
have acquired their immunity through the placenta which are absent 
in the young whose antibodies were conveyed through food. 
That changes in the blood serum may be caused by changed con- 
ditions in the tissues is further attested by many facts. For example, 
in pregnancy, the newly forming placenta may set free cells or cell- 
products which, sometimes at least, cause changes in the blood-serum 
of the mother, though the exact nature of these changes is in dispute. 
Romer, using the complement-fixation technique, found that the 
serum of adult human beings may possess antibodies for their own lens 
proteins. Bradley and Sansum, employing anaphylactic reactions, 
found that guinea-pigs injected with guinea-pig tissue-proteins (liver, 
heart, muscle, testicle, kidney) develop immunity reactions. Again 
during the late war, the type of toxic action to which anaphylactic 
shock conforms was found to exist after extensive injury of the soft 
tissues. It resulted apparently from the absorption of poisonous 
substances of tissue origin into the circulation. In fact, various cells 
and tissues when injured liberate such poisons, and even blood in clot- 
ting is known to acquire a transient toxicity of this type. 
With facts such as these before us, is it not a rational hypothesis 
to assume that changes in various parts of a body may on occasion 
influence the representatives of such parts in the germ-cells borne by 
that body? This appears all the more probable when we recall the 
