The exact nature of the poison is as yet uncertain, and as solanin is the only toxic principle so far discovered in potato, this has been held tentatively to be the essential cause. The amount of solanin in young and germinated potatoes has been given by Cornevin as follows:
| Germinated tubers | Young tubers. | |
|---|---|---|
| The entire tuber contains | 0.21 | 0.16 |
| The central fleshy part | 0.16 | 0.12 |
| The parings and pickings | 0.24 | 0.18 |
The toxic strength of the marc is not impaired by boiling, cooking or other culinary treatment, and the same is true of solanin. The toxicity is greatest after the potato has been subjected to germination, or when it has become green by exposure to the sun, and in these conditions the solanin is increased. The toxicity of the marc is higher in certain years, and in the product of certain fields, than in others, and this is in keeping with the effect of environment in modifying the products of a plant. The increased production of chlorophyl under the action of sunlight is associated with a material increase of the amount of solanin. Until therefore another toxic product can be shown to be the essential cause of this affection the solanin must be charged with this result. This conclusion would be more inviolable if the animals attacked showed other symptoms of solanin poisoning such as narcotism, vertigo, stupor and paralysis, and the absence of these may perhaps be due to the gradual advance of the toxic action, and the progressive immunizing of the animal system. The brain may be able to accommodate itself more readily than the skin.
The other constituents of the potato or of the marc fail to produce the eruption under other conditions: the alcohol in brewers and distillers’ grains, the acetic, lactic and butyric acids in the refuse of starch, beet sugar and canning factories, the potash in turnips and other roots, the yeast ferment in brewers’ grains. The acarus of foot mange (symbiotis bovis) is rarely present in the affected animal though the eruption in the same situation would strongly suggest its presence and lead to a search for it. Moreover the eczema appears at once in a large number of animals, affecting a large area without evidence of slow and steady progression and disappears with equal rapidity in many cases when the diet is changed. Finally the eczema has not been successfully propagated by inoculation which conveys mange infallibly from animal to animal.
Symptoms. The disease is associated with slight fever, costiveness, impaired appetite, hyperæmia of the mucosæ, epiphora, viscous salivation, muscular weakness, and finally emaciation and black diarrhœa. The gravity of these symptoms varies, being greater when the animals have eaten the leaves and stems, the raw potatoes in their skins, the young shoots and parings, or green potatoes which have been sunned. The animals may lie most of their time stretching themselves out with head extended on the ground, they may grind the teeth, may have pulse small and rapid, tympany, lethargy, coma and even paraplegia but these severe symptoms are exceptional and almost altogether confined to the cattle of distilleries which receive an exclusive diet of potato marc. In the pig and dog vomiting has been noticed (Cornevin). Pregnant animals may abort.
The local symptoms begin with redness and swelling of the skin around the pasterns, especially of the hind limbs, stiffness and a disposition to lie most of the time; then small flattened vesicles appear, isolated or confluent, which bursting, form extended, raw patches the abundant exudations of which concrete into thick crusts. The hairs stand erect and are abnormally thick at their roots. The eruption may extend to the whole limb, the scrotum, mamma, tail and body at large, so that in severe cases it is practically universal. The skin becomes thick, rigid, hide bound, wrinkled and folded with intervening cracks. As a rule, however, the eruption is confined to the limbs, scrotum, mammæ and tail. In some extensive and persistent cases the buccal mucosa suffers, particularly on the pad on the upper jaw, which shows extensive and irregular ulcers with purulent centre and swollen, congested margin. Abscesses may develop in the skin and subcutem and sloughing of the integument is not unknown.
Mortality is slight as a change of food is usually made and a recovery ensues in a few weeks. Yet Baranski noted 20 per cent. of deaths in Galicia, mostly in old, worn out animals which had been stabled for a length of time.
Lesions. On examination, post mortem, there are found hyperæmia and inflammation of the small intestine, some congestion of the cerebral meninges, and a red, bloody condition of the muscular system.
Treatment. The toxic provender must be stopped, or reduced to 20 or 30 litres of pulp daily, supplemented by sound wholesome dry fodder. Marker claims that 70 quarts daily of the potato marc may be given if combined with a fair ration of Indian corn. Turning out doors to pastures usually effects a speedy cure.
Local treatment is rarely demanded but when the irritation is great it may be soothed by bathing with cold or tepid water, lead lotion, glycerine and lead lotion, or by the application of ointments of lead, tar, oil of cade or birch, or carbolic acid. Dusting powders of zinc oxide, starch, lycopodium, boric and tannic acids may also be employed. Decoction of oak bark or solution of blue stone is often used, also creolin or cresol one part, to alcohol five parts.