280 SANITARY ENTOMOLOGY 



They did not find any substance wliich fulfilled all these conditions, 

 but found a soap (now known as the Panama larvicide) to meet most of 

 their requirements. This was made of the following ingredients : 



Resin 150 to 200 pounds 



Soda (caustic) 30 " 



Carbolic acid (sp. gr. 0.97) 150 gallons 



This makes a liquid soap which freely emulsifies with fresh water. 

 The carbolic acid must have at least 15 per cent of phenols and no 

 greater specific gravity than 0.97. 



This larvicide is manufactured as follows : Heat the carbolic acid 

 in a steel tank with steam coil. When steaming hot add the resin and 

 continuously stir the mixture by means of a paddle agitator until com- 

 plete solution is effected. Dissolve the caustic soda in 6 gallons of water 

 and add to the mixture. Heat and stir for five minutes. Draw a sample 

 and pour into water. If it emulsifies the process is complete, and the 

 product may be put into shipping drums which must be tightly closed. 



Oiling 



There are many ways of applying the oil. The most common method 

 is by knapsack sprayer or, where the ditch is along the road, by horse- 

 drawn tanks fitted with a spraying bar. For slow-moving water and 

 stagnant water, as well as the treatment of ruts, puddles, hoof prints, 

 and so forth, these methods are satisfactory. Dr. Metz found that 

 he got excellent results in boggy lands especially by applying a thin 

 mist of commercial creosote. A very small quantity will kill mosquito 

 larvse. 



For moving water there are many devices for maintaining a regular 

 dripping of oil from a suspended vessel upon the surface of the water. 

 Such devices can easily be rigged up by any practical man. Dr. M. J. 

 White of the Public Health Service modified this method by conducting 

 the oil to the water by means of a wick (Metz 1919). 



The war has brought about the new and even more efficient methods 

 of oiling which have been developed along many angles by Dr. W. L. 

 Mann, the Post Surgeon, and Lieut. E. C. Ebert of the Marine Corps at 

 Quantico, Va., with the assistance of Pharmacist's Mate Carl Duncan. 

 They have found that sawdust impregnated with crude oil will hold it for 

 a long time and will slowly give it up to the water. They therefore place 

 the sawdust impregnated with oil in a box and sink it in a flowing* stream 

 (fig. 60) ; or they throw a few grains of sawdust in a hoof print, or a 

 handful on a puddle ; or they fix a floating boom to hold back of it a 



