arthropod of unquestioned pathogenic significance do we now think that we have done with it once for all by a command that its breeding places shall be blotted out, or its natural enemies be let loose upon it. The business of medical entomology, as now understood, is, in the case of any species convicted on pathological evidence of being a standing danger to the public health, to unriddle its biology in every detail, and to investigate all the varying circumstances that influence its acquisition and retention of pathogenic capacity. The biological inquest must comprehend every stage of the creature's existence, from the egg to the engendering adult, and must include not only its affinities and its structure, but also its bionomy and its relations to environment. The bionomic inquiry must embrace the geographical distribution and seasonal incidence; the habits and the hours of activity; the powers and range of locomotion and the propensity to spread; the food preferences, the meteorological influences, and power of resisting vicissitudes of season and climate; the sexual instincts and fecundity; the mode of reproduction, breeding places and seasons, and the provision for larvæ; and the duration of life in every stage of development. If it be not a specific parasite, the bionomic investigation must also include the relations of the species to its environment, organic and inorganic, such as the physiographical and hydrographical features of the habitat, natural shelters, help givers, parasites, enemies and rivals. An excellent example of the range of the inquiry is furnished by Swynnerton's “Examination of the Tse-tse Problem," published in the Bulletin of Entomological Research for March, 1921. (See p. 22.) With the accumulation of exact information on all these points and the rational inferences drawn from it, medical entomology claims to be a science of practical application in preventive medicine-in short, a branch of Hygiene, and a branch which, although it finds its fullest and most constant application in those tropical countries where sanitary arrangements are still crude and imperfect, can not in the mutability of human affairs be neglected in any country. (Tropical Diseases Bulletin, vol. 18, No. 1, 1921, pp. 1-2.)

In this article we have considered in a far too summary way a dozen of the great discoveries in medical entomology, practically all of them made within the space of 25 years. Even to list the others would fill far more space than can be given here. Scientific laboratories were teeming with work of this kind down to the outbreak of the Great War in 1914. For the next four years many investigations were stopped. The men working in the sleeping-sickness problem in Africa, for example, had to abandon this work and join the military forces. Men from the laboratories in all the countries at war were sent to the front or to concentration camps to help in the care of the health of the troops. Many a promising investigator was killed. Printing facilities and postal facilities were so hampered that there was almost no news of the progress of investigations sent out from one country to another as in times of peace. None of the scientific men of the allied nations knew for several years what was being done by the trained investigators of the central powers. Nevertheless, the war gave a tremendous impetus to the study of medical entomology. Typhus in the Balkans and in Poland and Russia and in camps containing prisoners from those countries, the trench fever which soon developed alarmingly on the western front, and the spread of malaria

in nonmalarious regions of Germany, France, and even England, due to the infection of native anopheles by malaria-carrying soldiers returning from the fever-stricken fields of southeastern Europe, intensified the importance of the most careful and continued study of insect vectors of disease.

During the past 20 years the scientific world has thrown itself with ever-increasing activity into the great field opened by the initial discoveries. The greater importance of insect-borne diseases in the Tropics was immediately recognized, and England's great colonial possessions justified, and, in fact, necessitated, the founding of the great Schools of Tropical Medicine at Liverpool and London. A similar school was founded later at Hamburg by the German Government, but the loss of her tropical possesions has minimized the later work at this institution. Too much praise can hardly be given to the wonderful work done by the Oswaldo Cruz Institute at Rio de Janeiro. The corps of admirable investigators there has been increased from time to time and important discoveries have been made in the lines of medical entomology which the limited space allotted to this article prevents us from considering.

Medical entomology, however, is only a branch of tropical medicine, but it is a branch which absolutely requires the help, not only in investigation but also in teaching, of entomologists. A medical man, a trained pathologist, can hardly, after devoting years of research to other lines, become a skilled entomologist, since the field of entomology is so vast that to become skilled in any one of its many aspects requires a lifetime of work. This is coming to be realized. Not only must the taxonomy of insects engaged in the carriage of disease be critically studied, but their behavior under all possible conditions, their complete biology and ecology, their physiology, and many other things must be studied, and the man trained in so-called economic entomology is the one who must be called upon to suggest the best and most economical methods of suppressing these carriers.

Thus, there have grown up in many of our colleges and universities departments of medical entomology conducted jointly by entomologists and by medical men. At the Harvard Medical College a thoroughly competent entomologist gives instructions in medical entomology. At Cornell University, where there exists one of the strongest teaching corps of entomologists, especial instruction is given in this direction. The same may be said for the University of California, for the University of Wisconsin, and other institutions.

And excellent and comprehensive books on the subject of medical entomology have already been published, aside from numerous special books, such as those of the present writer, on mosquitoes and on the house fly, and those of the late Gordon Hewitt and Graham-Smith on

the house fly and other flies, and the excellent volume by LePrince and Orenstein on "Mosquito Control in Panama." As early as 1910, Prof. R. W. Doane, of Leland Stanford University, published a book entitled "Insects and Disease." This was followed by the excellent volume entitled "Handbook of Medical Entomology," published by Professors Riley and Johannsen, of Cornell University, in 1915; and by the excellent compendium entitled "Medical and Veterinary Entomology," by Dr. W. B. Herms, of the University of California, in the same year. Later Dr. A. C. Chandler, of the Oregon Agricultural College, published his admirable volume, "Animal Parasites and Human Disease," in 1918; an excellent volume entitled "Entomology for Medical Officers," by Lieut. Col. A. Alcock, Liverpool, 1920, and in the present year has appeared the very up-to-date volume entitled "Sanitary Entomology", edited by Dr. W. D. Pierce, formerly of the Bureau of Entomology at Washington. All of these works contain full bibliographies, and it will perhaps not be necessary to add a bibliographical list to this sketch.

A number of periodicals have also been started which are largely, and in some cases entirely, devoted to medical entomology.

The enormous and promising field is rapidly being exploited, and the more it is being worked the more obvious it becomes that an enormous fight is on between the human species and the class of insects which not only destroy his crops and damage most of his valued possessions but threaten his bodily health in a host of different ways.

The effect of these discoveries on the public health is already very apparent. Thousands upon thousands of lives have already been saved as their result. The intensity of many great scourges has been relieved. One of them, yellow fever, has measurably become a thing of the past. Gorgas's magnificent demonstration at Panama has shown that, so far as disease is concerned, the Tropics may be inhabited by the white race, and what that means for the future of the world no one can now estimate. All over the United States even, a country which is fortunately for the most part situated in the healthiest of climates, life on the average is longer and happier because of the knowledge that has been gained regarding insect-borne diseases. The American Public Health Association has borne its important part as an exploiter of these discoveries, as a publicist, as an influential apostle in the preaching of the new crusade.

In glancing through the fifty or more volumes of the publications of this society one is very greatly impressed by their high character. The whole series serves as an accurate record of the advance of preventive medicine in the United States, in Canada on the north, and in Mexico and the West Indies on the south. It is interesting to note, for example, the multitude of articles and reports on yellow fever

in the earlier volumes, these beginning with an admirable address in volume 1 by my old friend, Dr. J. M. Toner, now dead for many years. On reading this address I find many suggestive statements, suggestive in the light of later discoveries. But perhaps the most interesting article in the volumes, from the historical point of view, is the revolutionary paper read by Walter Reed in October, 1900, modestly entitled "A Note on the Etiology of Yellow Fever." Lazear had just died (September 25), and Reed, when calling upon me in passing through Washington on his way to the meeting, told me that he was making his first announcement before this association on account of its great activity in matters relative to the dread disease.

The list of investigators who have died for the public good in the course of the investigations we have been considering is already large. I have mentioned Lazear, Ricketts, McClintock, and McCray, and have shown that the deaths of Reed and Carroll occurred most prematurely shortly after their monumental discovery was announced As a fairly complete list of these martyrs of science is given in another chapter of this volume*, they need not be repeated here.

See footnote 1.

LAID AND WOVE.1

By DARD HUNTER.

[With 6 plates.]

All paper was formed in single sheets by hand before the invention of the paper-making machine. For the purpose of making handmade paper flat molds were used on which the pulp was deposited. This was accomplished either by pouring the liquid pulp upon the mold or by dipping the mold into a vat containing pulp. Through the centuries of paper making these molds have undergone many improvements and changes which have affected the character of the paper made on them to a marked degree. However, the molds used to-day for the forming of handmade sheets are based on the original principle of mold construction. To most paper makers and printers the two terms "laid" and "wove" mean little, aside from the fact that in the former the paper shows laid and chain lines when the sheet is held to the light, and in the latter the paper appears to have been woven, without much character or individuality.

The earliest paper was formed by the Chinese some 2,000 years ago on a woven cloth stretched over a bamboo frame which constituted the original paper-making mold. It is not known whether these first molds were dipped into the vat containing pulp or whether the fibrous liquid was poured upon them. As the wet sheet of pulp could not be taken from the cloth, the sheet was allowed to dry on the mold and was then removed. In this earliest form of paper making a great many molds were necessary if much paper was to be produced, for it would have required at least a day for each sheet to dry before it could be taken from the cloth covering of the mold.

It was left for an ancient Persian of genius to conceive the idea of a mold from which the wet sheet could be taken while still moist. This was the first real step in the progress of paper making, as this enabled the paper maker to make sheets continually from the same mold. For this purpose the mold had to be made from some smooth and firm material from which the wet sheet would free itself. These molds were made by placing many pieces of split bamboo or other

1 Reprinted by permission from The Printing Art, September, 1921.