ARE ACQUIRED CHARACTERS HEREDITARY? 469 



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 tlie 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 b}' 

 that body? This appears all the more probable when we recall the 



