THE LAMARCKIAN THEORY 415 



of individual tolerance for the habit-forming drugs is a case 

 commonly known. Ordinary poisons such as strychnine and 

 arsenic have a similar influence. They are used in minute quanti- 

 ties in medicine, and if these doses, tolerated by the normal 

 human bodj^, are gradually increased, a dose can ultimately be 

 administered without causing harm which would be sufficient to 

 kill a number of men if administered without previous preparation. 

 If such an extreme dosage is suddenly discontinued, the effects 

 are as serious as its sudden administration, but it can be reduced 

 gradually until the body is again able to get along without it. 



Functions of such organs as the eye are usually thought of in 

 terms of normal exercise and excess. It is true that excessive use 

 of the eyes frequently results in their impairment, but not less 

 true that reasonable use of the eyes results in increased power 

 of vision. Biologists who constantly use the microscope are likely 

 to use one eye to the exclusion of the other, either because of 

 natural preference or convenience in drawing or writing while 

 making observations, and it has often been noted that the eye 

 habitually used becomes much more effective for microscopic 

 observation. The converse cannot be demonstrated satisfactorily 

 in this case, for eyes when present, cannot often be wholly unused. 

 Such cases as the rudimentary eyes of moles and cave animals 

 are suggestive, but they require interpretation. 



The evidences of biology therefore support the first of Lamarck's 

 laws. We may definitely conclude that the use of functional 

 power brings about its increase, and disuse it decrease. The 

 matter of size is not necessarily a corollary of functional power, 

 and so is of fimited significance. 



The Inheritance of Acquired Characters. In fornmlating his sec- 

 ond law Lamarck made an unjustifiably positive statement. 

 No matter how confident we may feel that changes which appear 

 in individuals in response to environmental conditions may exert 

 an influence over future generations, we must admit that evidence 

 of such action is not available. The facts of palaeontology often 

 show such a gradual transition of phylogcnetic changes in correla- 

 tion with a changing environment that they almost convince us 

 of the potency of the environment in bringing about the evolution 

 of organisms, but careful consideration of such individual acquisi- 

 tions as are frequently produced will show that every generation 

 develops them anew; at birth there is no trace of the characters 



