tone” in all possible ways: The use of protective vaccines (Chap. XXX) appears to be advisable in such instances (colds, pneumonia after measles and influenza, inflammation of throat and middle ear following scarlet fever and measles). Results obtained in this country during the recent influenza epidemic have been conflicting but on the whole appear to show that preventive vaccination against _pneumonia liable to follow_ should be practiced. It would seem that among groups of individuals where infection may be expected the proper procedure would be to prepare autogenous vaccines (Chapter XXX) from members of the group and vaccinate all with the object of protecting them. II. B. (_d_) In this class come the “accidental carriers” like flies, fleas, lice, bed-bugs, ticks, and other biting and blood-sucking insects, vultures, buzzards, foxes, rats, and carrion-eating animals generally; pet animals in the household, etc. Here the animals are not susceptible to the given disease but become contaminated with the organisms and then through defilement of the food or drink or contact with individuals or with utensils pass the organisms on to the susceptible. Some biting and blood-sucking insects transmit the organisms through biting infected and non-infected animals successively. The spirilloses and trypanosomiases seem to be transmitted in this way, though there is evidence accumulating which may place these diseases in the next class. Anthrax is considered in some instances to be transmitted by flies and by vultures in the southern United States. Transmission of typhoid, dysentery, cholera and other diseases by flies is well established in man. Why not hog-cholera from farm to farm by flies, English sparrows, pigeons feeding, or by turkey buzzards? Though this would not be easy to prove, it seems reasonable. Preventing contact of such animals with the discharges or with the carcasses of those dead of the disease, destruction of insect carriers, screening and prevention of fly breeding are obvious protective measures. (_e_) In this class come certain diseases for which particular insects are necessary for the parasite in question, so that certain stages in its life history may be passed therein. The surest means for eradicating such diseases is the destruction of the insects concerned. Up to the present no _bacterial_ disease is known in which this condition exists, unless Rocky Mountain spotted fever and typhus fever shall prove to be due to bacteria. Such diseases are all due to protozoa. Among them are Texas fever, due to _Piroplasma bigeminum_ in this country which has been eradicated in entire districts by destruction of the cattle tick (_Margaropus annulatus_).