306 SECRETS OF ANIMAL LIFE 



most interesting contribution of the book is the 

 discussion of what Professor A'dami calls " the law 

 of habit." Once the cells of the body of a rabbit 

 have got accustomed to producing a counteractive 

 or anti-toxin to ricin (from the castor-oil plant), 

 they may go on producing anti-ricin for weeks or 

 months after the original stimulus. In the horse 

 a single toxin unit of tetanus can lead in the process 

 of immunization to the production of 1,000,000 anti- 

 toxin units. Ptyalism may persist for a year after 

 a dose of mercury. A cold in the head may con- 

 tinue for weeks after the causative agent has dis- 

 appeared and thorough sterilization of the nose has 

 been effected. The cells form a habit, it may be 

 an entirely new habit, and it lasts, " an acquired 

 cell variation becoming, if I may so express it, 

 converted into a cell heredity." In somewhat 

 the same way we may speak of microbes acquiring 

 new habits, for the indifferent bacillus may become 

 pathogenic, and the virulent may be tamed. But 

 tke difficulty is to pass from generations of cells 

 and of unicellulars to the very different case of 

 generations of multicellular animals. And even if 

 we suppose, with Professor Adami and others^ that 

 the peculiarly modified body-cells give off specific 

 metabolites, or hormones, or messengers of some 

 sort, which eventually reach their goal in the germ- 

 cell and thus specifically affect the offspring say 

 in the direction of becoming innately immune to 

 some poison can one say that this is as yet more 

 than a ballon d'essai? 



