tical reason why rat extermination could not be extended to entire cities or smaller communities through systematic repressive measures extending over a series of years. In this connection, it may be permissible to allude to the so-called Rodier method of rabbit and rat control, which depends simply upon systematic trapping and destruction of the females and the liberation of the males, since an excess of the latter, it is claimed, results in extermination or near extermination due to persistent persecution by the males. of the constantly decreasing number of females. It is based on the utilization of well-known habits to bring about self destruction of the species. The studies of bark beetles by Dr. Hopkins have shown the possibility of securing very efficient control by simply reducing their numbers, in some instances by 75 per cent., to such an extent that those remaining would be unable to overcome the natural resistance of the tree. This applies to enemies of living trees and presupposes that a minimum amount of injury must be inflicted or the attack can be successfully resisted. Were there sufficient incentive, it might be possible to go further with certain of these insects and bring about local extermination. A concrete application along these lines is found in the attempt of recent years by the United States Biological Survey to destroy predatory animals such as wolves and coyotes and thus eliminate in large measure the very heavy losses of western stock growers. The work is organized on a cooperative basis with states and local associations and as a consequence losses have been practically ended over great areas of the most valuable summer and winter sheep ranges and reduced in others to very small amounts compared with earlier years. The practical value of such work is evidenced by the fact that interested states, in order to cooperate with the government, appropriated over $200,000.00 for the fiscal year of 1922, in addition to increased contributions by stockmen as individuals and through their organizations. Already areas have been cleared or partly cleared of the pests and it would seem from the progress made entirely possible to exterminate the most destructive of these animals throughout the more important stock-raising areas at least, and this through the well directed efforts of a relatively small number of individuals. The systematic destruction of prairie dogs has resulted in over four million acres of public lands being "largely freed" from these pests. There has also been very effective work against pocket gophers and rabbits. It is within possibilities to make local and almost complete eradication absolute and thus in the course of years free large areas from serious pests. 40 THE SCIENTIFIC MONTHLY The work of W. F. Fiske upon the Tsetse Fly has shown that it is only necessary to reduce the infestation by this pest to moderate limits in order to secure a very satisfactory degree of freedom from the deadly sleeping sickness. The studies of Roubaud upon malaria in France indicate an intimate connection between this infection and the number of mosquitoes per host. The author suggests what he calls animal prophylaxis, that is, the importation of enough cattle in certain areas to attract the insects and thus protect man to a large extent. The keeping of rabbits has been advocated more recently as a protection from malaria, and may be regarded as a variant of Roubaud's plan. All are forms of percentage reduction, a step which under certain conditions might be continued to the vanishing point, at least, so far as the infection is concerned. Turning to the Acarina, we note the progressive extermination of the Cattle Tick from nearly 500,000 square miles of territory, and the consequent elimination from this area of a very serious infection. It was apparently an impossible undertaking until the decisive factors were ascertained. In this connection, it might be stated that gratifying progress has been made in demonstrating methods of controlling the Rocky Mountain spotted fever tick, a carrier of a deadly human infection. Even now plans are in progress to test the possibility of actually exterminating warble flies from large areas. This is somewhat different from the tick proposition. It appears to be within possibilities and is certainly worth a thorough test. The history of the larger animals shows a number of cases of extermination or near extermination as a result of continued adverse conditions, and in historic times this has been due mostly to systematic hunting or fishing, and usually it has been confined to a restricted portion of the range, though in some instances it occurred at a period which would permit the maximum reduction in the species, namely, just before the breeding season. The mere fact that a species occurs in immense numbers does not make extermination impossible, though it may greatly prolong the period during which adverse influences must operate. It is evident from a study of insects and an examination of the factors resulting in the extermination of larger animals, that relatively minor changes in environment or well organized attacks. limited to relatively few individuals or to comparatively restricted areas, may accomplish the apparently impossible. It is also evident that the elimination of a certain residuum may safely be left to the operation of various natural causes. This latter is an extremely important factor in any attempt to exterminate insects, since it is usually impossible to destroy the last individual or to bring about conditions over an infested area of some extent which would make the existence of insect life impossible. In view of the above, we believe that the problem of insect extermination should receive most careful consideration and as opportunity offers, tests or demonstrations should be undertaken in order to obtain more trustworthy data relative to possibilities in this line of repressive work. CITY PARKS AND PLAYGROUNDS AS THE By Dr. JAMES M. ANDERS PHILADELPHIA, PA. HE necessity for providing sufficient city parks and play spaces, including parkways and garden-streets, has been long appreciated by students of municipal sanitation and the truly enlightened part of the general public. We owe the existence of organized bodies for the purpose of promoting these agencies, all of which have been founded within the last half century, to a few leaders in the matter of community health and welfare and in civic advancement. As the result of their well-directed efforts considerable progress has been made in the important direction of providing an adequate proportion of open spaces in relation to the density and aggregate of municipal populations. Efforts to arouse public sentiment upon this vitally important question, however, should have received far greater encouragement than they did in the past. In this connection it should be recollected that in consequence of the free immigration of inferior races our national physique has shown up to now a slow and gradual retrogression. It is high time that an intelligent, concerted effort be made with the avowed purpose of arresting this physical decadence and, more than this, of beginning a new advance. To the student of hygienic and sanitary principles the sources of bodily and moral efficiency are not obscure, and with the aid of sufficient popular support he can indicate the remedies for the cure of the existing state of things with reference to our physical deficiencies. It will not prove difficult to show the connection of city parks and playgrounds with racial progress due to improvement in the national physique. Indeed, it is not too much to claim that a just appreciation of the beneficial effects of these breathing and play spaces of our cities would speedily lead to the acquisition of new areas and the development of land owned by cities for park and play purposes; this would mean a distinct advance in city building with reference to such questions as the number of houses to the acre, their proper grouping, and the extent of open spaces between units, as well as in street tree planting, all of which questions affect the health and strength of the community, as will be clear hereafter. war. The thirtieth annual report of the City Parks Association of Philadelphia sets forth the rôle played by the United States Government in physical demonstration of town planning on a large scale carried into execution in several localities, notably Yorkship, Portsmouth, N. H., and Wilmington, Del., during the recent Here was established a standard for city planning that it would have required a much longer period of time-quite a generation at least-to attain to in peace times. Attention should be directed to such government regulations as building ten to twenty feet back of the street line, fewer houses to the block and open space between adjoining houses, sixteen feet being the minimum. It is to be hoped that this example set by the government will not be lost, but will serve to inaugurate an era of decided progress in city building throughout our broad land. It is the duty of publicspirited citizens to see to it that modern town plans he adopted in connection with the future building of towns or settlements. True it is that out of appropriate town planning, as necessary sequences, grow hygienic and moral conditions which possess far-reaching influences for good. In other words, if our great American cities were models of city planning the effect would be not only greatly to increase real estate values, but also and more importantly to advance the essentials of human health and happiness. Confirmation of this statement is to be found in an article by Andrew Wright Crawford on "War Suburbs and War Cities," in which he quotes from a book by Charles Cadbury, Jr., the figures appended; they show the effect on children of the Garden Suburbs of Bournville, England, as compared with a ward in Birmingham, only twenty minutes away: An important project of city planning is that of zoning, which "expresses," to quote Herbert S. Swan in the American Architect, "the idea of orderliness in community development." The zone plan tends to strengthen and stabilize real estate values, in short |