Investigation of the air in malarious regions, however, has given result that tend to confirm the theory. Alaurel dis covered in such air an amceba that he failed to find in non-malarious air, and the discovery of similar amo3bEe in the nasal mucus he regarded as evidence that protozoa may be taken into the system by the respiration. Similar observations were made by Grassi and Calandruccio (Afannaberg), who discovered amcebfe in the nasal mucus of pigeons which for several nights they subjected to the ex halations from swamps or malarial earth.
It may be stated, however, that the evidence for and against the respiratory theory of infection is inconclusive, and that positive proof of either contention is still wanting.
3. Much attention has, of late, been given to tbe study of the skin as the probable channel through which infec tion by the malarial parasite takes place. It has been conclusively proved by in . 1 • \ tl . 1 th tun:, and in II Narieties of lia‘c inch a more or p.riod of incubation when 1 rotpz.lit ahout in this man fait has directed attention to — more particularly the means by which tik may be carried from in :7, .1 ...I uninfected persons. The most v • f such insects is, of course, the u! ,-.10:10. and the manner in which it n...v act as the intermediate host has I t,n the subject of much recent experi ntaron The plausibility of the inoculation tl ry is very much enhanced when com ns are made between malaria, and ? tl er parasitic blood-infections of man and the lower animals. It has recently been slim\ n by Bruce, for instance, that the tsetse Ily disease of Africa is due to a flagellate infusorium, and that the fly by feeding upon an animal already infeetcd and then biting a healthy ani mal will act as a carrier of the parasite from the infected to the uninfected. In Texas fever, shown by Theobald Smith to be due to a protozoon, another illus tration is afforded. In this disease the tiek Boi;philus boris) acts as the inter n ediate host. the tick falling from in fected animals gives birth to a numerous progeny. which, in turn, infect other ani mals feeding, in the pasture. (Sternberg, American Surg. Bull., April 10, '97.) It also well known that the Filaria Ranguinis hominis is carried from the sick to the well by the mosquito.
Ti ere are nlany circumstances associ ated ‘%ith the conditions under which malaria prevails that may be reconciled r ith the theory that the mosquito is an imjertant factor in the transmission of the j aras.ite. Thus. the relative im muhity possessed by those sleeping in the uj peT stories of a dwelling in a malarious re.fir.n is susceptible of explanation by
the limited extent to which the flight of mosquitos is elevated above the ground. Also. from the lessened resistance offered by the teuder skin of children tu the bites of insects may be explained the greater frequency m ith which they are infected by malaria in comparison to adults. It is only fair to state, however, that the advocates of the theory of in fection by the respiratory organs explain the greater liability of children as being due to the fact that they are nearer to the ground than those ot greater stature and arc therefore exposed to the infec tion in a more concentrated form. The fact that sleeping upon the ground in a malarious region renders a person par ticularly liable to infection may be for the reason that lie is thereby in a posi tion most likely to be bitten by insects. Further, it is well known that mosquitoes are unlikely to leave the region in which they are generated, and that as soon as a strong wind prevails they seek such shelter that the wind carries them for a limited distance only. This may explain the very short distance malaria is car ried by the inds.
Many interesting and valuable experi ments have recently been made relating to the part played by the mosquito in the transrnission of the malarial parasite. L. H. Warner (N. Y. Med. Jour., vol. lxviii, No. 24, Dec. 10, '93), in the study of this subject, bacteriologically exam ined various specimens of water obtained from the marshes of different malarious regions. In each specimen he found one or more forms of spirilla. These spirilla, however, produced no growth when in troduced into culture-tubes of blood serum and kept in an incubator from twenty-four to twenty-eight hours. Hu man blood was then collected from a number of persons by means of a steril ized hollow needle connected with the bulb of a syringe, also sterilized, and at once transferred to a blood-serum cult ure-tube, which was then placed in a thermostat and kept at a temperature of 100° F. A number of mosquitoes were then collected and kept in a sterilized bottle. From these by means of a plati num needle he extracted some of the albuminous poison with which mos quitoes are charged, and inserted some of it in each of the blood-serum cultures, which were then replaced in the thermo stat. Examination made after twenty four hours revealed a parasite not to be differentiated from the malarial parasite. As a. result of these experiments he be lieves the mosquito to be an important factor in infection.