1 882.] On Archcssthetism. . 455 



two following. The effects of use are well known. We cannot 

 use a muscle without increasing its bulk ; we cannot long use the 

 teeth in mastication without inducing a renewed deposit of den- 

 tine within the pulp-cavity to meet the encroachments of attrition. 

 The hands of the laborer are always larger than those of men of 

 other pursuits. Pathology furnishes us with a host of hyper- 

 trophies, exostoses, etc., produced by excessive use, or necessity 

 for increased means of performing excessive work. The ten- 

 dency, then, induced by use in the parent, is to add segments or 

 cells to the organ used. Use thus determines the locality of new 

 repetitions of parts already existing, and determines an increase 

 of growth force at the same time, by the increase of food always 

 accompanying increase of work done, in every animal. 



" But supposing there be no part or organ to use. Such must 

 have been the condition of every animal prior to the appearance 

 of an additional digit or limb or other useful element. It appears 

 to me that the cause of the determination of growth force is not 

 merely the irritation of the part or organ used by contact with 

 the objects of its use. This would seem to be the remote cause 

 of the deposit of dentine in the used tooth ; in the thickening 

 epidermis of the hand of the laborer ; in the wandering of the 

 lymph-cells to the scarified cornea of the frog in Cohnheim's ex- 

 periment. You cannot rub the sclerotica of the eye without pro- 

 ducing an expansion of the capillary arteries and corresponding 

 increase in the amount of nutritive fluid. But the case may be 

 different in the muscles and other organs (as the pigment cells of 

 reptiles and fishes) which are under the control of the volition of 

 the animal. Here, and in many other instances which might be 

 cited, it cannot be asserted that the nutrition of use is not under 

 the direct control of the will through the mediation of nerve force. 

 Therefore I am disposed to believe that growth force may be, 

 through the motive force of the animal, as readily determined to 

 a locality where an executive organ does not exist, as to the first 

 segment or cell of such an organ already commenced, and that 

 therefore effort is, in the order of time, the first factor in accelera- 

 tion." 



A difficulty in the way of this hypothesis, is the frequently 

 unyielding character of the structures of adult animals, and the 

 difficulty of bringing sufficient pressure to bear on them without 

 destroying life. But in fact the modifications must, in most in- 

 stances take place during the period of growth. It is well known 

 that the mental characteristics of the father are transmitted 

 through the spermatozooid, and that therefore the molecular 

 movements which produce the mechanism of such mental charac- 

 ters, must exist in the spermatozooid. But the material of the 

 spermatozooid is combined with that of the ovum, and the em- 



