36 VETEEINAEY TOXICOLOGY 



arsenic is united to organic groups, such as methyl and 

 phenyl, orders of toxicity down to practical inactivity, 

 dependent on the relative stability and resistance to reduc- 

 tion, have been noted. 



These considerations make it clear that for practice the 

 most dangerous arsenic preparations are those in which 

 the arsenious acid is in a readily soluble form, as in alkali 

 arsenite dips and weed-killers, and to a less degree with 

 copper arsenites and finely divided arsenious oxide. 



Absorption. — The absorption of arsenic is manifestly 

 intimately connected with the form of administration. As 

 stated, the coarsely powdered porcelain, or vitreous oxide, 

 appears to be without action on the dog, and according 

 to Kaufmann 45 to 60 grains of the dissolved oxide will kill 

 a horse, whereas 675 grains of the solid would be required. 



It is to be clearly remembered that solution is very slow 

 from the solid oxide in the digestive tract, and that, in 

 consequence, no exact connection between dosage and 

 effects of this form can be traced. It appears possible 

 — at any rate, it is worth investigation to ascertain — that 

 much of the alleged arsenic toleration in man and animals 

 is due to the fact that solid is taken, that absorption is very 

 slight, and that the greater part of the drug is excreted in 

 the faeces unchanged. Many of the conflicting statements as 

 to dosage and effect are due beyond question to the in- 

 adequate recognition of this fact. It must, however, be 

 remembered that by gradual dosage the horse acquires a 

 measure of tolerance. Thus, in the Holmes treatment after 

 a time 45 to 50 grains may be given against piroplasmosis, 

 surra, dourine, and other affections due to trypanosomes. 

 Moreover, Ehrlich has shown that strains of trypanosomes 

 can be bred which are immune to arsenic. 



In the dog, according to Henry Gray, long continued 

 small dosage is more likely to cause toxic effects than a few 

 large doses. After such prolonged dosage, irritation of the 

 conjunctivae, vomiting, and loss of appetite occur. 



Absorption of arsenious acid takes place slowly through 

 the intact skin. When introduced by a fresh wound, about 



