ISO LEO LOEB. 



So far we had only to deal with chemical not with structural 

 adaptations. It seems, however, possible to extend the preced- 

 ing considerations to structural adaptations. Ferments produce 

 primarily chemical changes. But we know of chemical ferment 

 actions which bring about structural changes in the medium in 

 which they act. Thrombin in transforming fibrinogen into fibrin 

 changes a colloidal fluid into a gelatinous more or less solid mass, 

 which under the influence of pressure and traction may show a 

 fibrillar structure not unlikely connective tissue. From a certain 

 point of view, the fibrin ferment may, therefore, be regarded as 

 a form producing ferment. 1 We might call it a morphogenic 

 ferment. We have reason to assume that there exist other mor- 

 phogenic ferments. So far mainly the splitting activity of fer- 

 ments has been studied. It is not unlikely that the action of 

 many enzymes may be reversible. There would then exist a 

 large number of enzymatic actions, leading to the building up of 

 complicated chemical compounds from relatively simple sub- 

 stances. Such an action would probably in part again be con- 

 nected with the creation of definite structures, which would be 

 different under the influence of different enzymes. These en- 

 zymes would have a specific species, and also a specific individual 

 character and the analogous products created by such ferments 

 would be different in different species and in different individuals. 



Such an interaction of substances with the resulting formation 

 of antibodies could especially be conceived of as taking place 

 during embryonic development ; it would tend to produce a cor- 

 relation between different chemical and structural mechanisms 

 which might in part at least account for the harmony which ex- 

 ists in the function and structure of different parts of an organism. 



It has not yet been investigated as far as I am aware, whether 

 some of the adaptations mentioned above have been acquired in 

 each individual or whether they are hereditary. That might be 

 doubtful, especially for instance in the case of the immunity of 

 scorpions and snakes against their own venom. The latter alter- 

 native is, however, very likely in the case of the anticoagulative 

 substance of the leech and of anchylostoma and in the case 



1 The fact that the fibrin ferment produces organized substance has already been 

 noted by Gautier. 



