44o THE POPULAR SCIENCE MONTHLY. 



Morbid variations of structure and function present three leading 

 phases of action, the acute, chronic, and diathetic. The primary causes 

 of each are the same, a faulty personal hygiene and an unfavorable 

 environment, but a derivative cause very generally predominates in 

 the heritage of a defect or taint in the blood. In acute variations the 

 struggle between the tendency to death and the tendency to reversion 

 is usually short and severe, but decisive. The contending forces are 

 often so nearly equal that a very little will turn the scale one way or 

 the other. Chronic variations only differ from acute in this, that they 

 are milder, or are more tolerable to the vital autonomy. The same 

 inherent principle struggles in each for the restoration of health, al- 

 though the process is not so impressively realized in the chronic as in 

 the acute form, by a rapid and well-defined course. What dissimilar- 

 ity there is in the two series of actions is wholly one of time and de- 

 gree, not of nature, the struggle between the tendency to health and 

 the tendency to disease presenting almost every conceivable phase of 

 activity, and lasting from a day to months or even years. 



As no one can say precisely when acute diseases end and chronic 

 begin, the distinction being arbitrary and accepted for convenience, 

 no more can any one say exactly when a slow disease is changed into 

 a diathesis. In fact, there are no sound reasons in support of the 

 opinion that such a change ever sharply occurs ; but there are in sup- 

 port of this, that a slow disorder is often gradually toned down until 

 it merges into a diathesis, when it is then known as a predisposition. 

 During the gradual disappearance of a slow disease one of untutored 

 and gross perceptions may decide recovery to be complete, while the 

 acute adept may be able to discern the manifestations of the disorder 

 subsequently for months. Indeed, there is scarcely any room for 

 doubt that, if our senses were far more acute, a diathesis or tendency 

 to some special disease would be disclosed in definite signs of imper- 

 fection, or of disorder. A diathesis is often seen gradually merging 

 into development, and development into a diathesis, and the frequency 

 with which this is seen to recur in the same person gives tone to the 

 conclusion that the letter state is only a very mild or occult phase of 

 the former. Any ordinary observer, with a predisposition to some dis- 

 order, is aware that very slight exciting causes usually serve sufficiently 

 to increase the imperceptible imperfection as to bring it within the 

 cognizance of the senses. But there is yet more indubitable evidence 

 that a series of morbid changes may be going on in the body of which 

 no cognizance can be taken. During the incubative stages of scarlet 

 fever, measles, small-pox, and syphilis, the contagium of each has a 

 definite period of maturative action before the signs of disease are in 

 any way apparent. When a wave of cold air sweeps over a continent 

 it develops in one a pneumonia, in another a rheumatism, in another a 

 fever or an attack of neuralgia, upon the great majority no bad effects- 

 whatever. Can it be doubted that some definite imperfection which 



