THE PHYSIOLOGY OF EXERCISE. 437 



certainly have tamed the beautiful zebra and quagga ; the elephant, 

 brought by Hannibal over the Alps, fell back with Northern Africa 

 into wildness. Only nutritive and formative augmentation of advan- 

 tages which an animal may have acquired in the wild state could 

 come into consideration here, and these would have to be hereditary to 

 lead to perfection in a course of generations. 



This seems, thirdly, not to come to pass. No matter for how many 

 generations man cuts off the tail and ears of dogs, tail and ears return 

 with each new brood. The mutilation which the Semitic races have 

 performed on their children for hundreds of ages, and which Islam has 

 imposed upon a great part of the population of the Old World, is not 

 yet chronicled in nature. If, now, artificial defects are not heredi- 

 tary, how may we venture to suppose that those artificially acquired 

 changes which appear as favorable results of exercise are conveyed 

 through egg and seed to posterity ? 



To this argument the following considerations are opposed: Al- 

 though deformities produced by exterior force are not inheritable, 

 we nevertheless see that incontestably internally acquired changes are 

 only too surely transmitted. Of this, the host of hereditary diseases 

 affords an example. Since cellular pathology has shown that the most 

 various heritable diseases of the tissues, the most malignant as well 

 as the most harmless forms, move within the limits of the once given 

 type, the difference appears exposed to light which separates an artifi- 

 cial deformity from a retrogression caused by disease ; and it becomes 

 comprehensible why in tame rabbits, the tips of the ears of which may 

 have been idle for many generations, the ear-muscles disappear, and the 

 ears hang down limp ; and why the eye and visory substance of subter- 

 ranean and cave-inhabiting animals waste away. But, even if a deterio- 

 ration within the type of the species by lack of exercise becomes heredi- 

 tary, formations dependent on nutritive and formative stimulation, 

 which also remain necessarily within the type of the species, may like- 

 wise be transmitted. This appears even to be the case with the inwork- 

 ing of the central nerve-system in certain forms of emotion, of which 

 the growing wild of the at first confiding bird on a formerly uninhabited 

 island furnishes a classical example. Certainly animals in freedom do 

 not, like those under human training, become habituated to definite, fre- 

 quently repeated functions, yet hunger and love, hatred, cold, thirst, etc., 

 drive them likewise to the frequent performance of certain acts. So ? 

 finally, might the innate superiority called instinct (Kunsttrieb) have 

 been gradually developed through practice, and the more easily, as a 

 certain degree of pleasure is connected with the execution of series of 

 movements that have become familiar. If, then, instinct does all that 

 is necessary for the maintenance of the species, there is no more room 

 for further improvement or for development in new directions, and the 

 species remains at the stage it has reached as bees and spiders have done 

 ever since man has known them. We may confidently assert that at 



