A very dilute arsenical solution also conserves the irritability of the excised nerve and muscle of the frog.

Considerable doses of arsenic given for a length of time produce fatty degeneration of the liver and other organs, and cause the glycogen to disappear from the liver, so that puncture of the fourth ventricle no longer produces glycosuria.

Minute doses of arsenic appear to increase the rapidity of the pulse. Larger doses diminish the pulse and blood-pressure. In frogs the heart is slowed, and finally stands still in diastole. This stoppage of the heart appears to be due to paralysis of the motor ganglia, as the muscular substance will still continue to contract upon direct irritation. In warm-blooded animals it appears to prolong the irritability of the heart, so that it will still continue to beat for many hours after the death of the animal. According to Kuntzer, this is due to retardation of the vital processes in the mammalian heart, so that it comes to resemble that of a coldblooded animal. In animals, arsenic has been found to diminish the blood-pressure from the beginning. This appears to be due partly to diminished activity of the heart, but chiefly to paralysis of the splanchnics allowing the abdominal vessels to dilate (p. 284). In frogs it produces apparent paralysis, but this appears rather due to diminished sensibility of the grey matter in the posterior cornua of the spinal cord than to real paralysis; for the nerves and muscles in this state are found to be still quite irrit-ahle, and although the animal is insensible to pinching it can and does move when laid on its back. As, according to Schiff, the muscular sensations are conveyed in the white substance of the posterior columns, this would appear to be unaffected, while the grey substance which conveys sensations of pain is completely paralysed (p. 160).

Fig. 169.   Vertical section of the healthy epidermis of a frog, a, Columnar layer of cells. b, Malpighian layer, c, Intermediate layer. e, Corneous layer.

Fig. 169. - Vertical section of the healthy epidermis of a frog, a, Columnar layer of cells. b, Malpighian layer, c, Intermediate layer. e, Corneous layer. f, Sheet of connective tissue forming boundary between dermis and epidermis. ( After Nunn.)

Fig. 170.   Vertical section of epidermis from a frog poisoned by arsenic. 6, vacuole in the softened protoplasm of the columnar layer of cells. At a the protoplasm is more softened and the vacuoles enlarged so that the cells are attached to the dermis only by threads of protoplasm.

Fig. 170. - Vertical section of epidermis from a frog poisoned by arsenic. 6, vacuole in the softened protoplasm of the columnar layer of cells. At a the protoplasm is more softened and the vacuoles enlarged so that the cells are attached to the dermis only by threads of protoplasm. (After Nunn.)

In some cases of poisoning by arsenic, paralysis of one or more limbs occurs after the acute symptoms have passed off. It usually affects the extensors more than the flexors, and is generally temporary, though it may be permanent.

The action of arsenic on the skin is peculiar. Ringer and Murrell noticed that in frogs poisoned by it the cuticle could be stripped off the whole body with the greatest readiness within a few hours after its administration. This condition was found by Nunn to depend upon softening of the protoplasm of the columnar layer of cells in the epidermis, so that the cuticle remained attached to the dermis only by a few protoplasmic threads (Figs. 169 and 170).

Other epithelial structures are also affected, and Cornil has found fatty degeneration of the epithelium lining the alveoli of the lungs in animals poisoned by arsenic (Fig. 171).

Arsenic is eliminated chiefly by the urine, and to a less extent by the bile, and slightly by the skin. Its elimination by the urine is very rapid.

Uses. - Arsenic has been used externally as a caustic application to cancers, and forms the basis of most of the secret 'cures' for this disease. The old recipe for this purpose consists of the following ingredients: Arsenious acid, 2 drachms; cinnabar, 2 drachms; ashes of old leather, 8 grains; dragon's blood, 12 grains, made into a paste with water or saliva.

Fig. 171.   Section of lung, hardened in osmic acid, from guinea pig poisoned by arsenious acid. The capillaries, v, project into the cavities of the alveoli, and are full of red blood corpuscles.

Fig. 171. - Section of lung, hardened in osmic acid, from guinea-pig poisoned by arsenious acid. The capillaries, v, project into the cavities of the alveoli, and are full of red blood-corpuscles. The protoplasm, a, of the cells is filled with fatty granules. The nuclei are well preserved. (After Cornil.)

In applying a paste of this sort it is advisable that it should consist of at least one-fifth of arsenic, and that it should not be applied to too large an extent of surface at a time. The arsenical paste used by Hebra consisted of arsenious acid 1 gramme, cinnabar 3 grains, and emollient ointment 24 grains.

Internally, arsenic is used for its local action on the intestinal canal as a tonic and astringent, for its action on tissue-change, and as a tonic and anti-spasmodic in cases of nervous disease. In the stomach, small doses stimulate the appetite, and are useful in allaying pain and checking vomiting. It may be given in irritative dyspepsia, in gastralgia, heartburn, in the vomiting of drunkards, and in gastric ulcer or cancer. It is also recommended by Ringer in cases of regurgitation of food unaccompanied by nausea. It is very useful in cases of diarrhoea where the tendency comes on during or immediately after the ingestion of food, whether in adults or children; it is then best given in small doses before meals (p. 387).