June, 1917.] ARSENICAL RESIDUES AFTER SPRAYING. 29 



fed on grain, hay and fresh vegetables, such as carrots and cab- 

 bage. At one time there was an epidemic of intestinal disorder 

 among some of the pigs; but on the whole they remained in good 

 condition, as shown by the record of the check pigs. 



The arsenate of lead used was from the same lot as that em- 

 ployed in the spraying experiments already recorded. The 

 amount constituting a dose was weighed out on chemists' bal- 

 ances and was fed directly to the pig by the attendant. Usually 

 the poison was inserted in a piece of carrot or other vegetable, 

 or was spread on a thin slice which was then folded over. The 

 piece of vegetable containing the poison was placed within the 

 pig's mouth and the attendant held him until he had chewed 

 it up and swallowed his portion. After a few experiences the 

 pigs usually accepted this treatment without special objection. 



THE UNIT DOSE CHOSEN. 



The amount of arsenate of lead selected as a unit of dose was 

 the average maximum per apple found in the analyses of sprayed 

 apples picked in ordinary manner before any intervening rain 

 as recorded earlier in this bulletin (see Table No. 3). This 

 average, if expressed as dry powdered lead arsenate analyzing 

 33.4 per cent AS2O6, was 1.7 milligrams. This amount of dry 

 lead arsenate, therefore, constituted the unit. All feeding was 

 of this unit or multiples thereof. 



In the series of pigs that were fed white arsenic, AS2O3, in-^ 

 stead of lead arsenate, an amount was used equivalent in arsenic 

 content to the unit of lead arsenate and the multiples thereof. 



In the three tables summarizing the results (see Tables Nos. 7 

 8 and 9), each horizontal line represents the feeding of one 

 guinea pig. The solid portions of the line indicate by their 

 thickness the relative amount of the poison fed to the pig. Thus, 

 the thinnest line indicates one unit daily. Progressively, the 

 heavier lines indicate 2, 3, 4, 7 units, and so on. The number 

 of units fed is shown by the figures at the end of each segment of 

 a line. The length of the solid portions of a line represents the 

 length of period thru which the pig received his daily dose of 

 the unit in question. The scale is stated at the top of each 

 table. The dotted portion of a line indicates a resting period, 

 during which the pig received no poison. The length of this 

 dotted portion of the line is drawn to the same scale. 



