Human Physiology. 343 



distinction between organic and functional diseases is scarcely 

 necessary. Every organic disease must be also functional; 

 every functional disease must be really organic, though there 

 may be no perceptible lesion or change in the part. And no 

 so-called functional disease can long exist without becoming 

 organic, and, in most cases, perceptibly so though changes in 

 the brain and nerves are often difficult and sometimes impos- 

 sible to detect. 



In the system of Dr. Farr, adopted by the Registrar-General, 

 diseases are divided into four classes, each including several 

 orders. Under Class I. Zymotic Diseases (zyme, a ferment,) 

 are included epidemic, endemic, and contagious diseases, and 

 those caused by specific poisons, and food or want of food. 

 The four orders are i. Miasmatic Diseases (tainted), as small- 

 pox, measles, scarlet fever, diphtheria, typhus and typhoid fevers, 

 cholera, ague, &c. Order 2. Enthetic Diseases (implanted), 

 as syphilis, gonorrhoea, glanders, hydrophobia, malignant pus- 

 tule, &c. Order 3. Dietic Diseases, as famine-fever, scurvy, 

 purpura, rickets, delirium tremens, and all the effects of stimu- 

 lants and narcotics. Order 4. Parasitic Diseases, as itch, 

 worms, ring-worm, scald-head, &c. 



Class II. Constitutional Diseases, containing two orders, 

 i. Diathetic Diseases, as gout, anemia, cancer, &c. ; and 2. Tu- 

 bercular Diseases, as scrofula, phthisis (tubercular consump- 

 tion), mesenteric disease, &c. These are, for the most part, 

 hereditary. 



Class III. Local Diseases, contains, order i. Diseases of 

 the Brain or Nervous System, as apoplexy, paralysis, epilepsy, 

 chorea (St. Vitus' dance), hysteria, mania, &c. 2. Diseases 

 of the Heart and Blood- Vessels. 3. Lung Diseases, as bron- 

 chitis, pneumonia, pleurisy, asthma, &c. 4. Diseases of the 

 Digestive System, as inflammations of the stomach or intestines, 

 jaundice, &c. ; and orders 5, 6, and 7 are diseases of the 

 kidneys, generative organs, bones, muscles, and skin. Class 



