604 ECZEMA. 



There is a further point to consider as regards the variation of 

 potato pulp in toxicity. Potatoes yield a more or less active residue, 

 according to the year in which they are grown, their state of germi- 

 nation, and the variety to which they belong. Raw or cooked potatoes 

 may produce eczema if given in large quantities or for long periods. 

 Numerous theories have been advanced as to the nature of the 

 morbid disturbance producing eczema. Some authorities declare the 

 appearance of the disease to be due to the presence of a toxic principle 

 contained in potatoes, viz., solanin. It might be objected that this 

 chemical principle only exists during germination while potatoes that 

 have not undergone germination produce the disease. Further, the 

 symptoms of poisoning by solanin differ from those of this form of 

 eczema, among which loss of appetite, for instance, or stuj^ef action, or 

 narcosis is never observable. 



According to other writers eczema is due to the action of the 

 lower alcohols contained in the refuse pulp, but again these pro- 

 perties exist in brewers' and distillers' grains, the consumption of 

 which produces no bad results. Similar objections might be made 

 regarding the suggested action of the acids of fermentation (lactic, 

 butyric, and acetic acids, etc.). 



Johne blames the salts of potassium, which, how^ever, can only act 

 as digestive irritants, and Ziirn suggests mycosic inflammation. 



Whatever the toxic principle, its effects are most marked in 

 animals undergoing fattening, and are rarely found in working oxen, 

 still more rarely in milch cows. In the last named the injurious 

 principle appears to be eliminated in the milk, and this theory is 

 supported by the fact that the liquid has purgative properties ; the 

 calves which consume it suffer from diarrhcea, which ceases when the 

 feeding is altered. 



Finally, it has been proved that different animals show different 

 degrees of susceptibility to the action of potato pulp. 



The symptoms do not appear until after tw^o or three weeks' feed- 

 ing on the potato pulp. Then the animals walk stiffly, rise with 

 difficulty, and display redness, swelling and sensitiveness of the limbs. 

 When the cedematous infiltration and reddening have become dis- 

 tinctly marked there appear, not only betw^een the claws, as in foot- 

 and-mouth disease, but over the entire limb and principally near the 

 folds of skin about the joints, numerous closely-packed small papules, 

 which in one or two days become transformed into vesicles through 

 exudation below the epidermis. 



This marks the eczematous phase properly so called. The vesicles 

 then become ruptured, the exuded matter glues the hairs together, 

 dries, and forms crusts, which have a peculiar and distinctive odour. 



