6o4 



SCIENTIFIC NEV\^S. 



[June 29, iS 



tinuous chart for each day. These and other improve- 

 ments help to give this form of recorder an advantage over 

 the one hitherto in use. It is, however, a rather more 

 expensive instrument. 



The photographic process used for sensitising the 

 charts is that know?n as the cyanotype, discovered by Sir 

 John Herschell in the early days of photography, but 

 slightly modified, in order to prevent the washing away of 

 the fainter tints of the trace in the process of fixing, 

 which is done simply by washing the charts for a few 

 minutes in cold water. It may be mentioned that the 

 charts are supplied ready prepared by the makers of the 

 instruments, Messrs. Negretti and Zambra, so that no 

 chemical operation is necessary on the part of the operator. 



DANGERS FROM FLIES. 



IT is rather an alarming fact that flies are winged 

 agents for spreading infectious diseases and para- 

 sitic germs. During the summer the swarms of flies 

 cannot be prevented from setting on any and every 

 object. They may alight on the expectorations of a con- 

 sumptive patient, or on the ejecta of a sufferer from 

 typhoid fever, and the next minute they may visit the 

 moist lips or eyes of a healthy human being. Their 

 feet, mouth, and breast have been in contact with an 

 infected mass, and they convey their poison to the 

 fresh and moist mucous membranes which are ready to 

 receive it. In Egypt, which is literally infested with 

 flies, diseases of the eyes are alarmingly carried by these 

 winged emissaries to the infant natives. 



The ejecta of the flies themselves are a source of ex- 

 treme danger in conveying disease. Every housekeeper 

 is irritated in the summer time when she sees the 

 mirrors and gilt frames spotted with the ejecta of the 

 flies. But Dr. Grassi, the celebrated Italian physician, 

 has by his experiments increased this irritation into 

 alarm. Between his laboratory and his kitchen there lies 

 a courtyard about forty feet in breadth ; on a plate on 

 the table of his laboratory he placed a large number of 

 the eggs of a human parasite. After a few hours he 

 found, on some white sheets of paper hanging in the 

 kitchen, the well-known spots produced by the excreta 

 of flies. These spots he examined with a powerful 

 microscope, and was astonished to find there several 

 eggs of the parasite which he had placed on the plate in 

 his laboratory. These had been conveyed by the flies 

 over the foriy-feet courtyard, and after passing through 

 their bodies, had been deposited — undestroyed — on the 

 white paper in the kitchen. 



Dr. Grassi then caught some of the flies which were 

 entering the kitchen window, and, on examination, he 

 found in their intestinal tract several of the eggs of the 

 parasite. Though satisfied with the result of his experi- 

 ment, he was alarmed at the risk which his family would 

 run, for it was practically impossible to keep all articles 

 of food from being touched by the flies. 



He next took some of the ripe segments of a tape-worm, 

 which had been in spirits of wine, and broke them up in 

 water containing sugar, so that a great number of the eggs 

 remained suspended in the fluid. The flies, attracted by the 

 sugar, came to the mixture, and in about half an hour the 

 eggs of the tape-worm were to be found in the excreted 

 spots and in their intestinal tracts. If these eggs had been 

 in a recent and living state, they would doubtless have 

 been just as easily carried. If any of our readers wish 

 to try an easy and safe experiment, get some lycopod 



powder, mixed with sugar and water, and after exposure 

 to the flies, the spores of the lycopod will be soon found 

 in the excreta, and easily detected by a common magni- 

 fying glass. 



It is very plain, then, that if the mouths of the flies 

 will admit of the introduction of such eggs and spores, 

 there will be no difficulty in their admitting scores of the 

 spores of parasitic fungi and eggs of parasitic animals. 

 This is an alarming source of spreading disease. Dr. 

 Grassi has detected in fly excreta the spores of the para- 

 site which is so fatal to the silk-worm. 



Some may think that the only real danger is from the 

 conveyance of the eggs and spores by the mouth, breast, 

 and feet of the flies. They may imagine that the active 

 digestion in the intestines of the flies will destroy the 

 vitality of the germs which have been swallowed. But 

 Dr. Grassi is of opinion that in many instances the 

 larger bodies swallowed do not serve as objects for 

 assimilation, but are got rid of, undigested, as foreign 

 bodies. He draws this conclusion from the fact that the 

 flies themselves fall victims to the growth of a parasitic 

 fungus, which is first taken into their own stomachs. . 



Such facts should be laid before the sanitary authorities 

 of our towns and villages, in the hope that every pre- 

 caution will be taken to minimise the possibility of the 

 transference of disease by the winged emissaries. No 

 doubt our modern sanitary arrangements have been 

 vastly improved ; and Britain cannot be put in the 

 same scale with Italy for the filth which engenders the 

 enormous swarms of flies. Yet the dangers to be 

 apprehended from the flies are possibly to be encountered 

 here, though in a less degree ; and the investigation of these 

 facts should be carried on by sanitary officers, with orders 

 to report the results of their experiments. 



Again, a distinguished surgeon. Dr. Finlay, of Havana, 

 has lately broached a theory corroborative of this — viz., 

 that mosquitos are actually spreaders of yellow fever. 

 His theory is that the sting of the insect, after penetra- 

 ing the skin of a yellow-fever patient, retains on its 

 exterior the germs of the disease, which may thus be 

 conveyed to the next person it attacks. As a result of 

 his investigations on the subject, carried on with great 

 care and untiring zeal, this observer found that every 

 mosquito that stings will probably deposit its inpreg- 

 nated eggs within a few days after its bite, provided it 

 can find water in which to deposit them. From these 

 eggs the young mosquitos will be developed in about 

 three weeks. As the eggs are deposited in the locality 

 where the mosquito stung its victim, the young would also 

 be produced there ; and, finding the yellow fever patient 

 near by, would sting him, become infected, and carry 

 the germs to other human beings. In fact. Dr. Finlay 

 believes that yellow fever is not transmitted through the 

 air, nor by contact, but only by inoculation, largely by 

 means of the mosquito. He regards the disease as 

 incapable of spreading wherever tropical mosquitos are 

 not found ; that it ceases to be an epidemic at the same 

 limits of temperature and altitude which check the 

 enemy's existence ; and that it spreads wherever the 

 mosquito abounds. In confirmation of his views, he 

 reports that, in the summer of 1885, mosquitos were 

 scarce in Havana, but were very numerous in the 

 autumn ; and that, although the summer was unusually 

 hot, yellow fever cases were few in number ; but in the 

 autumn these increased to an alarming extent. It is 

 humiliating for us to see how we frail creatures are 

 surrounded with so many sources of disease. 



