Obviously, all the propagation of disease by insects can be limited, though not entirely con trolled, by proper measures to destroy all ver min and insects and prevent their multiplication as well as their attacks upon human beings. Those living in mosquito-infected districts should be protected by screens, especially at night. The larva of the mosquito can be killed by the use of a small amount of crude petro leum, which spreads easily over the entire sur face of stagnant water. All pools, marshes and flowed lands should be drained, and the banks of ponds and streams should be altered so as to provide for a constant current of water, and obviate stagnation or occasionally flooded flats or margins. All water butts, eave-troughs and accidental receptacles of rain water should be emptied or treated liberally with chloride of lime. An epidemic of bubonic plague in San Francisco was terminated by killing the rats in the city.
Not unnaturally certain diseases are grouped together, as they occur largely during the first few years of existence, and during the last years of life, respectively, and are termed dis eases of childhood and diseases of old age.
The former aggregation includes measles, whooping cough, chickenpox, rotheln, mumps, scarlet fever, etc.; while the latter embraces arteriosclerosis, gout, deafness, cataract. etc.
See CHILDREN, DISEASES OF; OLD AGE, DIS EASES OF.
Diseases caused by perverted activity of the cell tissues are called gautogenous ; but they should no longer be considered in a group by themselves. A familiar example is auto-intoxication (q.v.), better termed intes tinal toxaemia, which is due to the retention in the colon and ileum of harmful bacteria, in gested with meat, fish and other albuminous food. Certain amino-acids are generated in the intestine which, being absorbed and car ried in the blood stream, cause severe headache as well as much damage to the blood vessels and the heart muscle. A very small quantity of animal food, or a meatless diet, causes a change in the intestinal flora which relieves the con dition.
Discoveries and Methods of Prevention.— The investigations of recent years have dis covered the origin of bubonic plague, as has been said, that scourge which since the Dark Ages has reaped its harvest of millions of human lives; they have revealed also the cause of the fatal sleeping sickness_, which is an organism carried by the tsetse fly to its millions of vic tims in Africa; also the pirochete of syphilis, that dread and deadly disease which Invades nearly all organs and tissues in the body. Had Ehrlich achieved nothing else, his life would have been a blessing and his memory immortal because of the invention of Salvarsan (q.v.), which in such a large proportion of cases checks or cures the luetic scourge. Flex ner's serum for treatment of cerebrospinal meningitis; the surely progressing conquest of hookworm disease among countless thousands of *poor and negroes, lazy and shiftless only because of prostrating anemia caused by the bloodsucking intestinal parasite (Nestor Americatuts); the discovery of the bacillus of typhus fever by Plotz, of New York, in 1915, and the signal success of the serum therapy (q.v.) thereupon devised; these stand as the
most brilliant achievements of a decade of years.
The forerunner of present day serum therapy was the use of diphtheria antitoxin, a procedure which has reduced the mortality of diphtheria from an average of 42 per cent to an average of 20 per cent, the deaths in some epidemics in cases in which the antitoxin was used falling as low as 12.5 per cent.
Vaccination against smallpox has been widely practiced as a protection and for minating epidemics and reducing their incidence to the minimum. See VACCINATION.
The use of derivatives of the *ductless glands,* suprarenal, thyroid, thymus, pituitary, corpus luteum and pineal gland, is increasing with the study of hemadenology, especially in certain anomalies of preadolescent life. Transitional, compensatory and abortive forms of pituitary disease, for example, are now recog nized, and the individual sufferers, through proper treatment, are saved from progressing to acromegaly, gigantism, infantilism, adiposis, sex inversion and eunuchism.
Through the careful study of foods and of metabolism, valuable discoveries have been made. Guelpa, of Paris, devised and suggested the system which Allen, of Rockefeller Institute, aided by study of Naunyn, has elaborated into a practical dietary which is largely successful in treating diabetes (q.v.), now known to be an expression of diminished functional capacity of the pancreatic islets.
Beriberi (q.v.), a nutritional disease con sisting of a multiple neuritis, characterized by a special train of symptoms, is very prevalent among sailors and natives of certain countries whose principal food is rice from which the pericarp has been removed. Restoration of the huilc of the grain prevents further exten sion of the disease, and this, with other dietary expedients, ameliorates rapidly the condition of the sufferers. In the recent uncovering of the cause of beriberi, a train of exploration was begun which resulted in 1911 in the dis covery, though not the isolation, by Casimir Funk, of the substances he calls €vitamines.° They may not be amines, but the name will serve. They are essential to health, resembling in that way the lipoids of . fats. Vitamines are found in meals, green vegetables, fruits and the ..pericarps of grain removed in milling for the sake of the appearance of the product. Pellagra (q.v.), a disease prevalent in the South, especially among negroes, character ized principally by muscular weakness, skin lesion and insanity, is a similar nutritional dis ease, in the opinion of most students, and is to be relieved by proper diet.