AS ILLUSTKATED BY THE POTATO MUKKAIN. 189 



necessarily, or at least most probably, arise under cultivation. 

 Their essence lies in a degeneration consisting in an abnormal 

 condition of the proteinous matters ; their cause in the mode 

 of cultivation ; the accidents inducing or accelerating the erup- 

 tion of the maladies, external, local, or temporary influences, as 

 very moist soil, peculiar weather, &c. 



This view of the essence of the disease consisting in a degene- 

 ration of the species is by no means new, though different from 

 the notions of all who have treated of the subject in its fulness 

 and the arguments on which it rests. The grounds which others 

 have built upon are generally merely local or confined. They 

 have adduced as causes of degeneration the circmnstance of 

 never renewing the crop from seed, the use of divided potatoes 

 or eyes as sets, the mode of keeping the sets during winter, 

 and other circumstances. Such views are, however, contradicted 

 by the fact that the circumstances were very different in the 

 different countries where the disease prevailed. In many places 

 the plants raised from seed were peculiarly subject to attack, 

 and besides published cases I can refer to one which occurred to 

 a clergyman at Jena who for a long time has paid particular 

 attention to this mode of raising potatoes. The disease has been 

 not less virulent where it has not been the custom to grow pota- 

 toes from sets. We must look then for some other cause. Such 

 notions, indeed, are of no avail except when to conceal ignorance 

 they are masked by such general expressions as debilitation of 

 potatoes, corruption of the juices, &c. The fact is incontestable, 

 that the disease is first manifested in the proteinous matters of 

 the cells, that they are relatively increased and altered in quality, 

 while the starch, on the contrary, is relatively diminished, and 

 also, though less decidedly, altered in quality ; that the relation 

 of the phosphates and alkalies is surprisingly changed. All 

 these circmnstances, however, according to late scientific im- 

 provements, are closely connected with each other, and no views 

 respecting the cause of disease can lay claim to any respect, 

 which do not at the same time at least show the possibility of this 

 especial result arising for the reasons assigned from chemical laws. 



On the contrary, this view is altogether calculated to verify 

 the required connexion, and to infer the result from the premises 

 not only as possible, but as probable, in a very high, if not 

 necessary degree. This view perfectly explains all the con- 

 flicting piienomena which have appeared during the expansion 

 of the disease, since it constantly places the outward circum- 

 stances which must naturally act differently on almost every 

 individual plant, in apposition with the inner specific tendency 

 to disease. It explains, moreover, perfectly the surprising 

 circumstance that in the same field — nay, even on one and the 



