REVIEW — TKOPICAIj MEniCINE, ETC. 75 



that the alum shall be distinctly basic. This is usually so in any case when the available Filters — 

 alumina exceeds 17-5 per cent. The following is the type of specification recommended : — continued 



The basic sulphate of alumiuri shall be guaranteed to coutain 17 per cent, of alumina (Al., O3), soluble in 

 water, and of this amount at least .5 per cent, shall be in excess of the amount theoretically necessary to combine 

 with the sulphuric acid present. It shall not contain more than 0-1 per cent, of matter insoluljle in water, and it 

 shall be practically free of chips and debris of all kinds. It shall not contain more than 0'5 per cent, of iron 

 (Fe„ O3), and the iron shall be preferably in the ferrous state. The alum shall be crushed to pieces of such a size 

 that they will pass through a ring three inches in diameter. 



If bidders so desire, they may bid on a, product containing a large amount of soluble alumina, stating, however, 

 the amount which they guarantee. The additional strength will be taken into account in deciding where to place 

 the order. 



Mention may be made of closed Candy filters, specially adapted for waters containing 

 iron ; and the Bell filters, which seem to be an adaptation of the American mechanical filter, 

 are closed, appear to be efficient bacteriologically, are easily cleaned, and are likely to have 

 a future before them as they are not very expensive. 



Smith' deals with modern methods of water filtration, considering first the sand 

 filter used both in the old manner and along with the " Howard" process, which consists 

 in running on to the surface of the filter a strong solution of aluminium sulphate at the 

 beginning of every filtering period, thus inducing a rapid formation of the so-called vital 

 layer. He also notes the spreading of the raw water over the filter bed by means of a 

 revolving sprinkler — a recent innovation. Secondly, he describes mechanical filters, 

 distinguishing four chief types — the Jewell, the Bell, the patent open and pressure filters 

 of Eeeves, containing quartz crystals, and the Candy filter. A warning is issued against the 

 use of any of these types without due precautions as to skilled oversight, etc. It is advisable 

 that such filters should be tested with the water which it is proposed to purify. 



As regards the question of domestic and public filters in Khartoum, see " Sanitary 

 Notes" (Third Eeport). 



Flies. Under this heading a few papers will be noticed dealing not only with biting 

 flies but with those flies which from their filthy feeding habits may carry disease germs. 



Austen- deals with the house-fly and certain allied species as disseminators of enteric 

 fever among troops in the field. He quotes Major Smith, who says : — 



an old idea of some Anglo-Indian sm-geons was that dysentery could be caught by using the same latrine as a 

 dysentery patient. There may be something in this. Experiments on animals have shown that the disease can be 

 inoculated per rectum. The ubiquitous fly may, therefore, be a dysentery incubator in open camp latrines. 



Enteric fever may possibly be conveyed in a similar manner, and Austen observes that 

 many cases of intestinal myiasis due to the larvifi of flies belonging to the genus Homalomyia 

 (H. canicidaris, Linn., and Soalaris, Fabr.), are probably to be traced to the parent flies 

 having oviposited on the anus when the patient has been using some country privy where 

 these flies are common. He then proceeds to describe the characteristics, life-history and 

 general bionomics of the commonest latrine-haunting flies, especially as regards South Africa. 

 He notes that Homahnnyia canicidaris is very often mistaken for Musca domestica, the true 

 house-fly, but it is smaller, narrower, and the fourth vein runs straight to the tip of the 

 wing instead of being bent up at an angle as in Musca. It is often called a " young house- 

 fly " by those who do not know that the larval stage is the period of growth in insects and 

 that no insect grows, in the true sense of the word, after attaining the perfect state. 



After dealing in detail with the house-fly, Austen mentions two other filth carriers, 

 the plum-coloured or metallic-green or bluish-green Pycnosoma flies, P. ■mai-yinale and 

 P. chlurupliijga, which also breed in decaying animal and excrementitious matter and 

 accordingly haunt latrines. 



Methods of preventing the access of flies to latrine trenches are given and a suggestion 

 made, that light metal covers, provided at regular intervals with apertures, closed by spring 

 flaps which could be actuated by the feet of the users, might prove useful, especially if 

 combined with the discharge into the trench of some such fluid as kerosine or crude creolin 

 in solution. 



1 Smith, W. R. (May, 190S), " Modern Methods of Water Filtration." Journal of tlie Koyal Institute of 

 Public Health, Vol. XVI., No. 5. 



= Austen, E. E. (June, 1904), "The House-Fly and Certain Allied Species as Disseminators of Enteric Fever 

 among Troops in the Field." Journal of the Royal Army Medical Corps, p. 651. 



