54 CAPT. LL. LLOYD. 



Table X. 

 Showing the Effect of Formaldehyde when available Water is strongly saline. 



Solution 



Conditions 



Total flies 



Percentages dead after : 



1 



3hrs. I 28 hrs. 48 hrs. 



Formaldehyde 

 10% in water 



Formaldehyde 

 10% in water 



Saturated with 

 salt solution 



Saturated with 

 fresh water 



29 

 21 



14 

 4 



69 93 



39 78 



and the conditions would approach those on board ship when it is not actually 

 raining. The results, which are given in Table XI, are very striking, as the flies 

 died rapidly when the available water was saline, and slowly when it was fresh. By 

 further experiment it was found that the flies drink as readily as water a solution 

 of 1 per cent, salt, that stronger solutions deter them, while 5 per cent, and upwards 

 repels them entirely. Formaldehyde properly neutralised and baited will be found 

 very efiective on board ship. 



Table XI. 



Showing the Probable Effect of Formaldehyde on Board Ship. 



Solution 



Formaldehyde j 

 7-5%, lime [^ 

 water 50%, I 

 sugar 5% / 



Conditions 



Salt water 



available 



Fresh water 



available 



Total flies 



94 



38 



Percentages dead after : 



2 hrs. 



22 

 3 



43 

 21 



hrs. 24 hrs. 



96 

 03 



The Strength of Formaidehyde to be used. 



The question as to the most effective strength of formaldehyde was approached 

 from tw^o points of view ; firstly, the stronger the solution the less likely are the 

 flies to drink much ; secondly, a little of a strong solution, or a large quantity of a 

 weak solution, will kill them. These will be discussed under the headings of " The 

 Deterrence of Formaldehyde " and "The Toxicity of Formaldehyde." The results 

 were then combined, giving the optimum concentration. At the same time control 

 experiments were made in cylinders as a check to the conclusion drawn. 



