Apkh. 24, 1908] 



SCIENCE 



657 



quite resistant to the action of the irrita- 

 ting substance. I know personally of a 

 number of individuals who have been able 

 since early childhood to handle poison ivy 

 with impunity, no dermatitis resulting 

 from contact with the fresh leaves. 

 Opinions differ much in regard to the ac- 

 quired immunity. Some people are ex- 

 tremely susceptible, the severest lesions fol- 

 lowing the slightest exposure. In many 

 instances it is claimed that no immunity 

 results from the first attack, a second, 

 third or even a fourth attack of dermatitis 

 occurring with painful regularity. A be- 

 lief is common, moreover, that these sub- 

 sequent attacks recur, without a second ex- 

 posure, at the same season in which the 

 first attack developed. There are, never- 

 theless, many cases in which a certain 

 degree of immunity develops, the severe 

 types of dermatitis never being reproduced, 

 the subsequent exposure bringing out only 

 a few vesicles and pustules on the skin. 



It is interesting to speculate whether 

 these cases of natural immunity are not 

 really examples of acquired immuwity, in- 

 dividuals in whom as children the effects 

 of handling the ivy have gradually worn 

 off, the original dermatitis having been so 

 insignificant as to have escaped notice or 

 being so many years distant as to be for- 

 gotten. 



There is some evidence also as to the 

 possibility of vaccinating against ivy 

 poisoning. The internal administration of 

 the tincture of Rhus toxicodendron is be- 

 lieved by many to completely prevent at- 

 tacks of this affection, and in the survey 

 for the Union Pacific Railway, when the line 

 was pushed through a wild country much 

 overgrown with the ivy, some of the engi- 

 neers discovered that by chewing and 

 swallowing the fresh leaves early in the 

 spring, they could ward off attacks during 

 the summer. It is stated that a similar 

 precautionary measure is resorted to in the 



Adirondack Mountains, where the plant is 

 so abundant as to be a troublesome pest. 



In conclusion we have in the Amanita 

 phalloides and in Rhus toxicodendron two 

 poisonous substances, acting in one case 

 upon the blood corpuscles, in the other 

 upon the epithelial cells of the skin and 

 kidney, in both of which the evidence at 

 hand points to a glucoside as the carrier 

 of the poisonous properties, and in both of 

 which active and passive immunity may be 

 experimentally produced. Whether these 

 observations have anything more than 

 theoretical value remains still to be de- 

 termined, a practical application of these 

 results being possible only when sera of 

 considerable antitoxic power can be ob- 

 tained from large animals. 



Yirtdence of Pneumococci in Relation to 

 Phagocytosis: E. C. Rosenow. 

 Virulent pneumococci do not absorb 

 opsonin from serum nor are they sus- 

 ceptible to phagocytosis, while non-viru- 

 lent pneumococci absorb opsonins and are 

 freely susceptible to phagocytosis. The 

 pneumococci isolated from the blood in 

 pneumonia resist phagocytosis in normal 

 and pneumonic blood, while those isolated 

 from the sputum are more susceptible and 

 show a correspondingly lower grade of 

 animal virulence. It seems that the pneu- 

 mococci in the blood in lobar pneumonia 

 are there because of their resistance to 

 opsonifieation and phagocytosis. 



The pneumococci isolated from the blood 

 of cases of pneumococcus endocarditis are 

 freely susceptible in vitro, to phagocytosis, 

 both in normal and homologous blood, and 

 yet in some way they are able to protect 

 themselves against the action of the leuco- 

 cyte and other cells in vivo because con- 

 stantly present in the circulating blood. 

 The recently isolated pneumococci in these 

 cases when grown in the homologous 

 serum from 24 to 48 hours instead of being 



