Polarity in Organic Elements. 365 



increase, grew into such forms as the essential nature of that matter 

 made necessary. The nature of this nutrient matter and the whole en- 

 vironment of the life germs, have remained practically the same from 

 the beginning of life, and the progress of forms consists of the gradual 

 combination of these elements of nutrition into organic bodies under the 

 stimulus of the physical forces. It is perfectly safe to affirm that if 

 the natural forces had been different, and the nutrient matter available 

 had been different, the forms of life would have been totally different 

 from what they are. If now these elements be artificially changed, 

 there is no end to the modification that might be produced, requiring the 

 time, however, of perhaps many human generations of effort directed to 

 a definite end. Such modifications might be effected by a different ar- 

 rangement of the molecules or cells to constitute the organ differently" 

 or by a fundamental change of the constitution of the cells themselves, 

 by a change of the nutritive food or composition of the cells. 



In man and the higher mammals the power of renewal is much re- 

 duced, and is limited to particular tissues, such as ( 1 ) " Those formed 

 entirely by nutritive repetition, like the blood and epithelia, (their 

 germs being continually generated anew in the ordinary condition of the 

 body). (2) Those of lowest organization, and of lowest chemical 

 character, as the gelatinous tissues, the areolar and tendinous, 'and the 

 bones. ( 3 ) Those which are inserted in other tissues not as essential 

 to their structure, but as accessories, as connecting or incorporating them 

 with the other structures of vegetative or animal life, such as nerve 

 fibres or blood vessels. ( Carpenter s Human Physiology. ) The repair- 

 ing processes are much more active in the lower than in the higher ani- 

 mals, and much more active in the } 7 oung than in the old. Numerous 

 authorities have been produced to show that there have been cases of 

 ' < spontaneous amputation " of limbs in foetal life, and a subsequent 

 partial renewal of the same, < ' and it seems probable, from the history 

 of normal development, that in the cases in which perfect hands and 

 feet have been present without the corresponding limbs, these hands 

 and feet have been secondary productions from the stumps of ampu- 

 tated limbs, since any original defect of development would have af- 

 fected the hands and feet, rather than the arms and legs." ( Carpenter.) 

 There is one instance on record ' ' of the twice repeated production of 

 a supernumerary thumb, after it had been twice completely removed ; 

 and one case in which the whole of one ramus of the lower jaw having 

 been lost by disease in a young girl, the jaw had been completely re- 

 generated, and teeth were developed and occupied their normal situa- 

 tions in it." 



Morbid growths are thought, by Carpenter and others, to be due to 

 morbid constituents in the blood, which automatically form themselves 



