656 



SCIENCE 



[N. S. Vol. XXVII. No. 695 



is made and employed in a number of 

 affections by a certain group of medical 

 men. Pfaff had previously pointed out 

 tbat the internal administration of toxico- 

 dendrol to rabbits killed them at the end 

 of 12-15 days by nephritis, although some 

 animals died in convulsions within the 

 first 24 hours. The subcutaneous inocula- 

 tion of the fluid extract of Rhus toxico- 

 dendron produced in rabbits an intense 

 nephritis with large quantities of albumin 

 and many casts in the urine, the animals 

 dying ia from 8 to 15 days. Rarely some 

 of the rabbits died in convulsions on the 

 first day. The effects of the fluid extract 

 being identical with those described by 

 Pfaff for toxicodendrol, there could be no 

 doubt that this extract contained the ac- 

 tive principle. In addition to the neph- 

 ritis, a huge necrosis and slough developed 

 at the site of the subcutaneous inoculation. 

 Guinea-pigs are more susceptible to the 

 poison than rabbits, a small quantity pro- 

 ducing a similar local necrosis and neph- 

 ritis. The fatal dose for rabbits varies 

 from one half to two cubic centimeters, 

 and for guinea-pigs from one fourth to one 

 half cubic centimeter. With both species, 

 if small doses be given at first, followed 

 by increasing doses at appropriate inter- 

 vals, active immunity can be established. 

 Large quantities of the fluid extract can 

 eventually be given, three to four cubic 

 centimeters in guinea-pigs and eight to ten 

 cubic centimeters in rabbits, in both cases 

 representing a considerable multiple of a 

 minimum fatal dose. The time of the 

 dosage must be carefully graduated, the 

 most favorable interval between the periods 

 of administration being apparently ten to 

 twelve days, corresponding to about the 

 period of incubation. With low multiples 

 of a fatal dose, the animals react well, 

 develop no local lesions, and can be kept 

 alive almost indefinitely, no late mani- 

 festations of intoxication appearing. If 



too large quantities be given, the animals 

 die of nephritis, and occasionally local 

 lesions are found. In general, however, 

 the local action of the poison on the epi- 

 thelial cells of the skin is less likely to ap- 

 pear during immunization than the de- 

 struction of the kidney cells. 



The serum from these actively immu- 

 nized animals will confer passive immunity 

 upon other animals. For these experi- 

 ments guinea-pigs were always selected 

 because of their more regular suscepti- 

 bility. The poison and serum must be 

 administered separately to avoid the pre- 

 cipitation of the serum by the alcohol in 

 the fluid extract, and even in the severe test 

 of giving both doses at the same time the 

 serum will completely neutralize the 

 poison. In certain instances by this 

 method of testing, one cubic centimeter of 

 serum neutralized five or six fatal doses 

 for guinea-pigs. When the effects of the 

 Rhus toxicodendron are not completely 

 obviated, the test animals die of nephritis. 

 Careful dissection of the skin at the site of 

 inoculation shows no necrosis or slough.^^ 



In connection with the effect of Rhus 

 toxicodendron upon the kidney in the pro- 

 duction of active and passive immunity, 

 it may be mentioned that the only human 

 beings who have died as a result of iA^y 

 poisoning have apparently succumbed to 

 kidney affections. 



Large animals can also be immunized; 

 a fifty-pound goat was eventually given 

 twenty cubic centimeters without the de- 

 velopment of subcutaneous lesions or 

 nephritis. 



Finally, it is interesting to inquire 

 whether natural immunity to poison ivy 

 occurs in man, and whether immunity 

 develops after recovery from its effects. 

 In regard to the first point, there is no 

 difficulty in showing that many persons are 



^ Ford, The Journal of Infectious Diseases, Vol. 

 4, No. 4, November, 1907. 



J 



