This section is from the book "A Guide To The Poisonous Plants And Weed Seeds Of Canada And The Northern United States", by Robert Boyd Thomson, H. B. Sifton. Also available from Amazon: A guide to the poisonous plants and weed seeds of Canada and the northern United States.
The primary reason for this publication is the long-felt need of a text-book to accompany the course on poisonous plants which is given the students of the Ontario Veterinary College. This object has been kept constantly in mind. It has necessitated the preparation of a book at a price within the reach of every student, and yet one that contains in easily available form an up-to-date knowledge of our common poisonous plants, the characteristics by which they may be recognized, the symptoms produced by them and the remedial treatment required. It is hoped that the book will also prove useful to the veterinarian who is in practice, the farmer, the stockman and, to a more limited extent, the medical practitioner and the public generally.
In arranging the work, a departure has been made from the usual practice. To facilitate the determination of the plant responsible in a given case of poisoning, the book has been divided into four sections. In the first three are included the plants that are mainly responsible for fatalities among animals. These are grouped on the basis of their source in the animal's feed, whether found in hay (Section I), in pasture (Section II), or in concentrated feedstuffs (Section III). A word may be added regarding Section III, since so far as the authors are aware this is the first time that the importance of poisonous plant constituents in concentrated feedstuffs has been given recognition in a text-book. Micro-analytical methods have lately been extended to determine the presence in such feedstuffs of poisonous material that eludes the ordinary chemical analysis. As a result, it has been found that poisonous seeds in injurious quantities have been included with great frequency in our commercial feeds, giving rise to fatalities and disease, the cause of which was hitherto unsuspected. The loss in Canada has been so great that, after thorough investigation, the Department of Agriculture has designed a new feedstuffs act with a view to its prevention, and established a micro-analytical laboratory for the enforcement of the statute. In the fourth Section are grouped the plants that, although poisonous, rarely cause the death of animals. It comprises by far the largest number, including some that are the source of medicinal drugs, others that have large amounts of virulent poison, and many that are poisonous only if taken in quantity - all not sufficiently attractive to animals to be the source of much danger. Previously considerable confusion resulted from bulking, without discrimination, all the plants that contain poison. It is hoped that the arrangement followed in this book will be found of practical value, by avoiding this difficulty and rendering the determination of the plant easier. The medical profession should find Section IV of most interest since the plants that are mainly responsible for poisoning in man are collected here. (See p. 109.)
The illustrations are from photographs and drawings made especially for the book. By means of these and by the classification into the groups above referred to, it should be possible for an amateur to identify the plant sponsible in an ordinary case of poisoning. No key based on botanical characters has been included, since such a key would be impracticable because of confusion with the numerous non-poisonous forms. At the end of the book, however, a "symptoms" key has been added. Such a key cannot, in the present state of our knowledge, be made precise. Its purpose is merely to facilitate diagnosis by suggesting the plants that should be looked for when certain symptoms are observed and plant poisoning is suspected.
A word may not be inopportune on the need of research on poisonous plants. The indefiniteness with which many statements have had to be made and the dearth of positive experimental work upon which to base conclusions have been keenly felt in the preparation of these pages. Two lines of attack are evident, one based on the detailed chemical analysis of the poisonous plant, the other on feeding experiments with the plants themselves. These two lines are complementary and both very necessary. The toxic substance having been determined, it is often at once evident what the chemical antidote should be. Moreover, much is known or could be easily learned of the conditions of its action. For example, how much is immediately apparent when it is known that prussic acid is the chemical responsible for Cherry or Sorghum poisoning. Knowing the volatile character of this toxic substance we can at once see why the dried fodder is harmless. Again, when the chemical responsible for Hemlock poisoning was found to be polymerized by heat much of the erratic character of the poisoning in this case was understood. It was quite evident why this plant was less dangerous in the heat of summer. Still all the emphasis must not be placed on this line of research, essential though chemical analysis assuredly is. The constitution of a plant is exceedingly complex and several factors may co-operate in producing the poisonous effects. As mechanical injury in the case of Skunk-tail Grass opens the way for bacterial infection, so in the case of Horsetail poisoning, it is quite possible that irritation of the digestive tract by the indigestible silica may pave the way for the attack of a chemically poisonous substance. It is thus only by feeding experiments, approaching the natural conditions as nearly as possible, that final and dependable results can be obtained. A creditable beginning has been made both in the United States and in Canada. Such work along physiological lines should be continued as well as research on the poisonous plants from the chemical standpoint. This is the immediate need. After proper antidotes and treatment have been discovered, however, there still remain two problems - one in connection with the utilization of the highly complex organic products that some of these weeds* contain, products that are very difficult to form synthetically in our chemical laboratories; and the other concerned with the elimination of the weeds themselves from our grain fields, pastures, parks and ranges. The importance of such work to the community at large war rants a comprehensive plan of attack and ample government support.
No bibliography has been compiled. This service has been admirably performed in Pammel's "Manual of Poisonous Plants," and Long's "Plants Poisonous to Livestock," which should be consulted by everyone wishing to make a more special study of the subject. References to these books and the many publications of the various agricultural departments and colleges will be made throughout the work.
The authors wish to express their indebtedness to Professor N. C. Hart, of Western University, and Miss M. V. McCulloch, of the Botany Department, University of Toronto, for contributions to the illustrations, and to Miss Jane McGillicuddy for help in the preparation of the text. Dr. C. D. McGilvray, Principal of the Ontario Veterinary College, kindly consented to read the original manuscript, and his suggestive criticisms have been much appreciated.
*An industrial use has already been found for Wild Mustard, Brassica arvensis, the seed of which is being separated from grain screenings by special machinery and utilized on a commercial scale, at the same time improving the screenings for feeding purposes.
R. B. Thomson. H. B. Sifton.
University of Toronto, January, 1922.