20 THE CAUSATION OF DISEASE. 



1. By insufficient, excessive, or improper ingesta. The 

 latter, of course, includes poisons, germinal or otherwise. 



2. By disease of the blood-plasma-forming tissues — i.e., 

 those organs which convert the ingesta into suitable food for 

 the cells. 



3. By inhalation of insufficient or of nocuous matters, 

 mechanical, germinal, or gaseous ; also imperfect exhalation of 

 lung excreta. The temperature and dampness of the atmo- 

 sphere may also exert an ill effect upon the body. 



4. By disease of the blood-cell-forming organs. 



5. By disease of the respiratory organs. 



6. By disease of the vascular system : Heart, blood-vessels,, 

 and their nervous regulating systems. 



7. By disease of the excretory organs : the cell sewage not 

 being properly drained off, the cell-E contains matters injurious- 

 to life. 



8. By direct nervous influence upon cells. The striking of 

 a nervous impulse upon a cell constitutes a modification of 

 E, since the influence comes from without. In this way the 

 muscle dynamite is exploded, and the zymogen of the gland 

 converted into zyme, w T hile the direct influence of the nervous 

 system upon cellular elements is abundantly shown in the 

 field of pathology. 



Since every tissue and system is dominated by the nervous 

 system, we see how T potently it may control the individual 

 cell-E's. Thus the vascular, the excretory, the respiratory 

 system, &c, are under its direct control. 



These considerations should prepare us for the fact that the 

 nervous system plays an enormous role in the 'phenomena of 

 disease. 



9. By injurious influence upon the exterior of the body — 

 e.g., violence, extremes of temperature, filth, parasites. 



Now, if one tissue is capable of modifying the environment 

 of another, it is obvious that disease in one tissue may set up 

 disease in another, and this again in a third, and so on. 

 Disease in a complex organism, such as man, is thus often 

 a very complicated process. 



All the tissues of the body are in fact knit together into one 

 physiological whole, so that if a disease originates in any tissue; 



