June, 1917.] ARSENICAL RESIDUES AFTER SPRAYING. 27 



Summary. 



1 . Lead arsenate, used as an insecticide or spray on fruit trees, is suflaciently 

 soluble in human gastric juice to cause lead and arsenic poisoning. Measures 

 must, therefore, be taken to remove this spray from the fruit. 



2. The presence of apple pulp appears to slightly increase the solubility of 

 the lead arsenate in the human gastric juice, probably owing to the organic 

 acids in the pulp. 



3. Milk mixed with the gastric juice in the proportion of 1-1 practically 

 prevents solution of the lead arsenate, probably by neutralization and fixation 

 of the free hydrochloric acid. 



DISCUSSION. 



The conclusion offered in the second sentence of the first 

 paragraph of the summary just quoted should be understood as 

 that of Drs. Carlson and Woelfel and not that of the writers of 

 this bulletin. Our own conclusions, as will be noted elsewhere, 

 may be somewhat differently expressed. 



Unfortunately, there are, apparently, no records showing the 

 solubility of ordinary white arsenic AS2O3 in gastric juice. Com- 

 menting on this point in a letter to the writer, December 1, 1914, 

 Dr. A. J. Carlson says: 



''I do not know of any actual determination of the solubility 

 of white arsenic (AS2O3) in gastric juice. It is quite soluble in 

 cold water (1 part in 30 to 80), more soluble in hot water, and still 

 more soluble in hydrochloric acid. It is clear from the above that 

 in the following mixture: 0.5 grams AS2O3 plus 25 cc. gastric 

 juice, plus 25 cc. water, at 38° C. for 10 hours, all of the arsenic 

 would go in solution. You ought to find that lead arsenate is 

 less toxic than white arsenic (AS2O3)." 



In another letter, dated November 20, 1914, Dr. Carlson writes: 



"Since lead arsenate is not, to my knowledge, used in thera- 

 peutics, there is probably no figure available in the matter of 

 exact toxic dose. Could you not determine it approximately 

 on rabbits or dogs, by running parallel series with arsenic and 

 lead arsenate? You can then compute the doses of lead arsenate 

 for man on the AS2O3 basis. 



"Speaking as a physiologist interested in public health I 

 should say the question is not how much of the poison may be 

 ingested without producing acute or obvious chronic symptoms, 

 but how completely can man be safeguarded against even traces 

 of the poison. There is no question in my mind that even in less 



