THE LAW OF HABIT 55 



ment of a completely new technique in our Army Service now 

 that all soldiers are inoculated against typhoid and the two 

 paratyphoid fevers. As Major Dreyer has more particularly 

 emphasized, the mere fact of agglutination is no longer of any 

 diagnostic value. The whole army agglutinates the specific 

 bacilli of all three diseases. Smallpox, naturally acquired, 

 usually confers a lifelong immunity ; vaccination, as conferring 

 a mild and modified disease with lessened general reaction, 

 confers immunity for five years or so, although with each repeti- 

 tion of the vaccination the indications are that the period of 

 immunity is materially lengthened. 



Now we know that the leucocytes (which evidently are the 

 cells most concerned in the production of " antibodies ") have 

 but a short period of active existence : once they pass into the 

 blood they do not multiply there. We must therefore con- 

 clude that the toxins in the first place act upon the mother or 

 germ cells of the lymph nodules and bone marrow, that these 

 gain the new powers and pass them on to successive generations 

 of daughter cells. The same principle must obtain for other 

 active cells of the body. 



The Law of Habit 



Here we observe the working of a law which to my know- 

 ledge, if recognized, has not been dealt with adequately by the 

 biologists in general, a law which, it may be, is coming into the 

 ken of the physical chemists in their studies upon the effects of 

 recurrent stresses upon the crystalline structure of steel and 

 other metals. In a notable address delivered in 1896 Weigert, 1 

 the Frankfort pathologist, laid down the law of inertia, the law 

 that once a cell is stimulated to perform a certain act it con- 

 tinues to perform that act for some time after the stimulus has 

 ceased to act. Fraser Harris, 2 now Professor of Physiology at 

 Halifax, Nova Scotia, in 1900 took up the subject more fully, 

 calling attention to the inertia of rest, as exemplified by the 

 latent period of stimulated muscle, as well as the inertia of 

 active function. For myself there is here something beyond 



1 Deutsch. med. Wochenschr., 1896, 635. See also Gesammelte Abhandlungen, 

 1906, 1. 



2 British Medical Journal, 1900, ii. 741, and The Functional Inertia of 

 Living Matter, London, Churchill, 1908. 



