244 ON VARIABILITY AND ADAPTATION 



therefore it betokened something unusual. It was a portent, 

 but its effect was temporary. People spoke of it after it was 

 gone ; as it were, a condition of inertia continued with steadily 

 diminishing force after the stimulus had passed away. Then by 

 chance in the seventeenth century a comet came into the ken of 

 an astronomer who, through his special knowledge, was, if we 

 may so express it, peculiarly responsive ; its presence stimulated 

 him to a more than ordinary degree. He looked up the earlier 

 records and found that a similar comet had been reported as 

 flaming into prominence at regular intervals. This led him 

 further to study the path of the comet, and not merely to deter- 

 mine the course of this one comet, but that of other comets and 

 of meteorites in general. And now everybody knows all about 

 comets, can predict their return ; the series of observations of 

 this one astronomer, Halley, has permanently and continuously 

 affected civilized man. 



So it is with the cell molecules. One particular stimulus 

 may have but a temporary effect ; another, acting upon the cell 

 in a particular state, may initiate a particular recurrent cycle 

 of intracellular changes, may set up a habit. 



Not all influences upon cells will set in action these recurrent 

 and cyclic changes, but undoubtedly the dominant constituents 

 of cells, the proteins, by their very nature and complexity of 

 structure, favour the development of cell habits. Let me 

 illustrate. A diffusible foreign body, itself of proteid affinities, 

 gains entrance into the blood a toxin ; and, provided that 

 it be not exhibited in excessive amount, it is in the first place 

 neutralized, and next leads to the presence in the blood of anti- 

 toxins. We know that the toxins gain entry into the cells ; 

 know that the cells, or certain of them, actively discharge anti- 

 toxins. There may have been not a sign of specific antitoxins 

 in the body fluids primarily, but now they are produced in 

 abundance in amounts far in excess of the amount of toxin 

 introduced. If at first they were modifications of the toxins 

 introduced, brought about by cell activity, certainly the later 

 crop cannot be of this nature. And here is the point : they 

 continue to be produced days and weeks after the original toxins 

 have been neutralized or destroyed. 



It may be that our presumption is wrong, that the toxin 

 molecules, once within the cell, persist there, acting as enzymes 



