234 Theories Treating of Inheritance 
out the organism are likewise undergoing continual 
change, and because of these changes in relations new 
conformations become produced at each stage of the 
developmental process in a variety becoming ever more 
complex.” 178 
Nevertheless this does not hinder one, according to 
that investigator, from considering the organism in its 
entirety as a single physiological unit because of the idio- 
plasmic identity of the nuclei of all its cells;—a thing 
which he thinks, makes the inheritance of acquired 
characters conceivable.179 
For to explain the latter, Hertwig brings up the cases 
of infection, immunization, and other similar examples, 
in relation to which the organism can really be regarded 
as a single entity. He quotes for instance the experi- 
ments of Ehrlich who has succeeded by the administration 
of extremely small doses of ricin in making rats immune 
to this poison which is very powerful for them, and in 
establishing the fact that this immunity was acquired not 
only by the walls of the digestive canal with which the 
poison comes into immediate contact, but also by all the 
other tissues of the body, such as for example the sub- 
cutaneous tissues and the ocular conjunctiva, and even 
by the germ cells as was proved by the fact of the trans- 
mission of this immunity to the young born of immunized 
parents. 18° 
Just as all the cells of the body are accessible to the 
action of ricin and thanks to that fact all undergo a 
material modification, which some of them, namely the: 
germ cells, transmit later to the descendants as an im- 
*8Oscar Hertwig: Die Zelle und die Gewcbe. II. P. 75, 144, 156. 
Oscar Hertwig: Ibid. II. P. 241. 
*°Oscar Hertwig: Ibid. I]. P. 24cff. 
