INTRODUCTION. 



Section I. 

 THE NATURE OF DISEASE. 



I. Limitation of the Conception of Disease. 



Our first task is evidently the necessity for defining the province of 

 which we will treat and for expounding what we understand by the term 

 "Disease." 



If we call "sick" only those cases in which the organism undergoes such 

 a disturbance in its functions that its existence seems threatened, we will be 

 in a dilemma when we consider the changing developmental forms of our 

 cultivated plants, for we will then discover that the above explanation is in- 

 sufficient. We know, for example, that our species of cabbage, kohlrabi and 

 cauliflower are descended from a plant similar to bank-cress which, in its 

 natural development as a wild plant, shows no tendency toward the forma- 

 tion of large leaf-buds such as cabbage heads, nor of root-like swellings of 

 the stem, as kohlrabi. These vegetables have been produced by selection and 

 cultivation and are characterized by a condition which we term parenchy- 

 matosis, because the woody elements have been replaced by a tender 

 parenchyma, due to the high degree of nitrogen continuously supplied from 

 generation to generation. In dry, hot summers young plants grown on soils 

 poor in food materials begin to show a marked ripening and, in connection 

 with this, a reddish blue tone in their leaves. In case kohlrabi, under such con- 

 ditions, makes any development worth mentioning, it becomes "stringy," 

 that is, its flesh is traversed by tough, hard fibres, making it "woody." Investi- 

 gation shows that the kohlrabi plant by the curtailment of the supply of water 

 and food materials is well on the way toward again developing a wood-ring 

 with prosenchymatic elements, as found constantly in the wild plant. Very 

 similar conditions are found in carrots in which our normal uncultivated 

 plant possesses a solid woody root, rich in starch. Our cultivated varieties, 

 on the contrary, have become thick, fleshy structures; the best containing no 

 starch at all but the greatest possible amount of sugar. Only in the so-called 

 fodder varieties, aS; for example, the white giant carrot, is still shown an 

 abundance of starch. Hofllmann-Giessen has experimentally developed our 

 cultivated carrot back to the wild form. 



Now, is the cultivated form a diseased condition since it actually suc- 

 cumbs more easily to certain disturbing influences, or is the reversion of the 



