226 BACTERIOLOGY. 



tract. It is therefore the internal condition of 

 the organism, of its organs, tissues or cells, that 

 alone determines the character of the effect. 

 The impulse that must come from outside 

 to produce these effects is called the stimulus. 

 Hence there must exist a fundamental internal 

 organization, that is to say, a predisposition to 

 something external. Since also the physio- 

 logical manifestations remain the same, while 

 the character of the stimulus varies, the true 

 cause of the manifestations must lie in this in- 

 ternal organization. The intrinsic predispo- 

 sition is physiologically the true and sufficient 

 cause, and therefore the sole cause of the nor- 

 mal processes of life. On this side Virchow 

 and Brown indeed recognized the fact that a 

 quantitative excess in a normal stimulus may 

 be the cause of disease ; too much light, for 

 example, produces blindness. The effect of a 

 stimulus may likewise be too great if the natu- 

 ral predisposition of the organism be too feeble, 

 although the stimulus itself is still within 

 physiological limits for a normal organism. 

 Disease, then, may be regarded as the effect 

 produced by quantitative changes in normal 

 conditions, either when the physiological organ- 

 ization is too feeble or the stimulus too intense. 

 Apparently, at least, infectious diseases which 

 were presumed to introduce an entirely new 



