17 



will exist in the absence of free water I'or a much long-er period tliau 

 is realh^ thi^ case. In the opinion of the writer, wliere the mud drie,'? 

 up entirely the mosquito larx.e are necessarily killed, but that they 

 may exist in yery wet mud for a longer or short(>r time is true. 



An interesting obseryation liearing upon this point has been made 

 by Dr. St. George Gray, of Castries, St. Lucia, British AVest Indies, 

 and reported in the Journal of Tropical Medicine, London, May 15, 

 1900. He says that on February 7, 1900, he examined a spot wherc^ he 

 had obtained larya' of ^Vnopheles a few months before. The pool had 

 been dr}^ for three weeks, hardly any rain having fallen during that 

 time. The surface of the mud at the bottom was cracked and dr^-, 

 although soft enough under thi^. crust. He put the nmd into a clean 

 pickle bottle and put al)out 3 inches of filtered water oyer it, but there 

 was no result. He also took some grass from the sides of the pool and 

 put that grass into another pickle bottle, adding 3 inches of filtered 

 water. On the following morning he found a few minute larya^ 

 wriggling about in this l)ottle. These rapidly grew in size, and he 

 soon had a half dozen healthy looking larysi? in his ])ottle. On the !:}lst, 

 a fortnight after he had taken the grass from the sides of the pool, he 

 reared the imago of Culex tmnkitus. From this observation he argues 

 that some species of Culex, at any rate, do not always lay their eggs 

 on the surface of the water, but where they will be washed into the 

 pool by the first heavy rain. Other similar experiments were failures. 

 This record is a very interesting one, but, like all isolated observations, 

 needs verification.'^ It may here be mentioned that Drs. J. W. W. 

 Stephens and S. R. Christophers, in their article on '"The distribution 

 of Anopheles in Sierra Leone," published in the reports of the malarial 

 committee to the Royal Society (London, July 0, 1900), stated that 

 they were unal)le to hatch the eggs of Anopheles after desiccation oh 

 blotting paper for more than forty-eight hours, although they hatched 

 after twenty-four and forty -eight hours' drying, respectively. 



The number of specie n of mosquitoes. — As regards the different kinds 

 of mosquitoes, about 250 species are known, of which only about 30 

 have been found in the United States. These are divided into 5 differ- 

 ent genera, each of which will receive consideration in the following 

 pages. Of the malarial genus Anopheles, Mr. F. V. Theobald writes 

 us there are 27 species in the British Museum collection. 



MOSQUITOES AND MALARIA. 



This is not the place to discuss at length the history of the discover- 

 ies which have brought about the very perfect proof that mosquitoes 

 may and do transfer the malaria germ from a malaria patient and 



^Dr. "Walter Reed, U. S. A., tells me that Dr. Lazear has just made a similar 

 observation in Cuba. 



8495— No. 25- Oo 3 



