142 LEO LOEB. 



ternal, as adaptations of one part of the body to another part of 

 the same organism and adaptations of an organism or of one of its 

 constituent parts to the outer world, although these two kinds of 

 adaptations must not necessarily be regarded as sharply distinct, 

 inasmuch as it can be assumed that external conditions cause a 

 primary internal reaction, which gives rise to a secondary internal 

 change, the latter possessing the character of an adaptation and 

 therefore representing directly an internal, indirectly however an 

 external adaptation. 



It appears possible to connect certain characters, whose use- 

 fulness for the organism possessing them, seems to justify their 

 classification among the adaptive phenomena with other facts 

 which have been found by the experimental study of immunity. 

 A few adaptations of this kind may be selected to demonstrate 

 this connection. In the tissues of vertebrates and invertebrates, 

 substances are present which have a strongly accelerating effect 

 upon the coagulation of the blood. If a wound is made and the 

 blood escapes, the contact with these tissues has a tendency to 

 stop the bleeding and prevent the animal from bleeding to death. 

 The tissues of each class of animals are especially adapted to the 

 fibrinogen of their own blood. The blood of a bird coagulates 

 more quickly under the influence of the tissue of a bird than of 

 a dog or of a frog. The blood of a turtle coagulates more 

 quickly under the influence of the tissues of a turtle than of the 

 tissues of a mammal or of a bird. The same holds good of 

 frogs' blood. Invertebrate blood, like that of a lobster, is not at 

 all influenced by the tissues of vertebrates, but very powerfully 

 so by the tissues of the lobster and to a less degree by the tis- 

 sues of some other invertebrates. Here we have apparently to 

 deal with a specific adaptation. A certain relationship exists be- 

 tween blood and tissues of one class of animals ; a specific rela- 

 tionship, which proves very beneficial to the animal. A some- 

 what analogous fact is mentioned by Duclaux. He states that 

 it is well known to manufacturers of dairy products that the milk 

 of a certain species of animals is more rapidly coagulated by the 

 rennin of the same than of another species. 1 



1 Although the analogy between these two facts is clear, the usefulness apparent 

 in the case of the tissue coagulins, seems to be absent in the case of the specificity of 

 rennin. The latter fact can therefore not be included among the phenomena of 

 adaptation. 



