30 



0. vexans remains below for longer periods ; and Aedes cinereus 

 is more often found below than above. In-the case of A. macnlipennis 

 this may be due to its long lateral bristles making swimming beneath 

 the surface difficult. In the case of the three other species the oxygen 

 content of the water may influence them. The functions of these 

 bristles should be studied. Their removal renders swimming at the 

 surface difficult, and causes severe injury, soon followed by death. 



Aedes cinereus is found in clean water only, 0. vexans perhaps prefers 

 dirty water and Cnlex pipiens occurs in very dirty puddles, rain- 

 water casks, etc. 



Anopheles plumbeus is the most interesting of the 3 German Ano- 

 phelines from a biological point of view. In the forests it attacks 

 man from 8 a.m. onwards in warm weather during July and August. 

 Even in cool weather it bites in the mid-day hours. It never occurs 

 in stables with A. macnlipennis and A. bifurcatus, and is even more 

 an out-door species than the latter. A captive female oviposited on 

 wet blotting paper instead of on water, and died within 18 minutes 

 of depositing the first egg. Probably, therefore, it oviposits on the 

 edge of the breeding-place in tree-holes, the eggs hatching when heavy 

 rain raises the water-level. It is probable tlrat hibernation takes place 

 at such places in the egg-stage. 



Theohaldia morsitans is not known to bite in Germany, but appears 

 to feed on avian blood. In the Mannheim woods when shelters for wild 

 birds were examined, numerous gorged examples of T. morsitans were 

 found, with a few A. macnlipennis and A. bifurcatus, and two females 

 of Culex hortensis (the other non-biting German species). 



LuTRARio ( — ). Note sur I'Emploi de I'Acide cyanhydrique dans les 

 Services de Prophylaxie. — Bull. Office Intemai. d'Hvg. Publique, 

 Paris, xii, no. 5, May 1920, pp. 484-492, 1 plan, 1 chart. 



In experiments with gaseous reagents chloropicrin and phosgene 

 were found unsatisfactory. » Chloropicrin is slow in action on rodents, 

 3 hours at 1-07 c.c. per cu.^metre being necessary to kill them, fleas 

 are not affected by it and a ''special generator is required. Phosgene 

 at the rate of 1 gram of the liquid per cu. metre kills rats and fleas 

 in about 1 hour, but in damp places this gas rapidly decomposes and 

 loses all its efficiency ; it has the further disadvantage of corroding 

 metals. 



With hydrocyanic acid gas 2\ grams of sodium cyanide per cu. 

 metre of space are recommended ; this will kill all rats and their 

 fleas in 1 hr. 45 min. Thirty minutes ventilation should suffice after 

 fumigation, but 1 hour is safer. 



An indicator that will give a reaction in a dilution of 1 part of HCN 

 in 3 million of air is prepared by dipping paper in a 3-4 per cent, 

 solution of guiacum resin in alcohol. The paper is dried, and when 

 required for use it is sensitised with a 1 per cent, solution of copper 

 sulphate. 



Apart from the cost of the Clayton apparatus necessary for fumigation 

 with sulphurous anhydride, the cost of the hydrocyanic acid method 

 is only about half as much. 



An entirely successful result was obtained at Venice, where a grain 

 elevator with a content of 350,000 cu. metres and containing 25,000 

 tons of grain was fumigated against rats and their fleas, sodium cyanide 

 at the rate of 2| grams per cu. metre being used. Double this 

 strength was found efficient against all stages of Pediculns humanns 



