MAIN HBRARY.AG'RlCL»L.TUR*foef»T. BIOLOGY LIBRARY HOG CHOLERA THE MACMILLAN COMPANY NEW YORK • BOSTON • CHICAGO • DALLAS ATLANTA • SAN FRANCISCO MACMILLAN & CO., LIMITED LONDON • BOMBAY • CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, LTD. TORONTO HOG CHOLERA ITS NATURE AND CONTROL BY RAYMOND R. £IRCH, B.S., D.V.M., Pn.D. PROFESSOR IN CHARGE OF THE NEW YORK STATE VETERINARY COLLEGE EXPERIMENT STATION AT CORNELL UNIVERSITY, ITHACA, NEW YORK gotft THE MACMILLAN COMPANY 1922 All rights reserved PRINTED IN THE UNITED STATES OF AMERICA COPYRIGHT, 1922, BT THE MACMILLAN COMPANY. Set up and printed. Published September, 1922. . Press of J. J. Little & Ives Company New York, U. S. A. PREFACE My object in preparing this book has been to place in the hands of those who handle hog cholera definite and authoritative information regarding the disease. There are abundant publications dealing with hog cholera but for the most part they consist of technical papers covering certain restricted phases of the disease, or of attempts to circumscribe the entire subject in the scope of a few pages. Neither meets the needs of the man who must handle hog cholera in the field. More- over these publications appear as bulletins or as special papers in technical journals, and usually they are not at the veterinarian's command at the time he needs them. We are rapidly discarding the old belief that any one who can use a hypodermic syringe can cope with hog cholera. Questions constantly arise regarding diagnosis, complications, when or whether to immunize, which method to use, the subsequent care of the herd, the handling of young pigs, slaughtering from infected herds under inspection, and many other individual prob- lems. The effective handling of hog cholera, like the handling of other diseases, is founded on exact knowledge of tlie malady itself, but hog cholera differs from other in- fectious diseases in that preventive vaccination against it has served to open the new field of swine practice. v 498438 VI PREFACE The result is that there are many veterinarians who will not attempt to cope with the disease, or who, making the attempt, feel the need for guidance. This volume is in no sense a compilation. For the most part it reflects personal experiences gained during ten years of intimate contact with hog cholera in the capacity of practicing and consulting veterinarian, anti- hog-cholera serum producer and research worker, but acknowledgment is due many other members of the veterinary profession whose researches and observations have revealed many of the foundation facts on which the subject matter rests. For statistical and other data I have consulted other authors freely, relying for sta- tistics especially on the numerous and excellent publi- cations of the United States Bureau of Animal Industry. I am indebted to Dr. E. A. Cahill, Director of the Pit- man-Moore Biological Laboratories, Zionsville, Indiana, for some of the illustrations. Dr. V. A. Moore, Dean of the New York State Veteri- nary College at Cornell University, and Dr. J. W. Benner of the College Experiment Station Staff have read the manuscript, and each has offered many valuable sug- gestions which are deeply appreciated. Great care has been taken to make the book a conserva- tive and accurate guide for the practicing veterinarian who must accept farm conditions as he finds them and handle hog cholera so as to secure and retain the con- fidence of his clients. If among other imperfections there are departures from this ideal I trust that my readers will direct my attention to them. R. R. B. CONTENTS CHAPTER I HISTORY AND ECONOMIC IMPORTANCE . . , . 1 II NATURE AND CAUSE OF HOG CHOLERA .... 7 III METHODS OF DISSEMINATION 17 IV COMPLICATIONS 21 V SYMPTOMS AND LESIONS 35 VI DIAGNOSIS, DIFFERENTIAL DIAGNOSIS, PROGNOSIS 58 VII PREPARATION OF ANTI-HOG-CHOLERA SERUM AND HOG CHOLERA VIRUS 76 VIII METHODS OF USING ANTI-HOG-CHOLERA SERUM . 118 IX HANDLING HOG CHOLERA IN THE FIELD . . . 158 X HOG CHOLERA, MEAT INSPECTION AND GARBAGE FEEDING 197 XI CONTROL AND ERADICATION OF HOG CHOLERA 230 ILLUSTRATIONS PAGE 1. Shoats affected with acute hog cholera 37 2. Lung of pig showing ecchymoses due to acute hog cholera 46 3. Left auricle of pig's heart showing petechise due to acute hog cholera 48 4. Spleens showing hemorrhages which are rather typ- ical of acute hog cholera 49 5. Kidney of pig showing numerous petechiae due to acute hog cholera 51 6. Lymph glands of pig showing hemorrhages caused by acute hog cholera 54 7. Bleeding room in anti-hog-cholera serum laboratory. (Courtesy Pitman-Moore Biological Laboratories) 77 8. Corner of anti-hog-cholera serum laboratory. New York State Veterinary College at Cornell Uni- versity 79 9. Post-mortem room where autopsies on virus pigs are held 88 10. A close view showing the hypering process ... 91 11. Bleeding unit, and hog prepared for bleeding . . 99 12. Bleeding for serum . . . . . . -. . . . 101 13. J Testing anti-hog-cholera serum 107 14. Injecting anti-hog-cholera serum in the ham . . . 119 ix ILLUSTRATIONS 15. Method of holding shoat for injecting serum in axillary space 120 16. An improvised method of holding shoats for immun- izing 121 17. Convenient hog holder made from % inch gas pipe, and flexible clothes wire 123 18. Method of preparing snout rope for confining large hogs 124 19. Method of noosing the snout of hog 125 20. Injecting serum behind the ear 129 HOG CHOLERA CHAPTER I HISTORY AND ECONOMIC IMPORTANCE HOG cholera seems to have appeared first on American soil in 1833, at which time an outbreak of the disease was reported in the Ohio valley. It is not definitely known whether the malady orig- inated in this country or in Europe, but it is a rather significant fact that the wild hog has flourished in Eurasia, and not in North America, in spite of the fact that the fauna of the two continents are in most other respects very closely related. It is also of special significance that the earliest authentic report we have of the disease in this country was made at a time when railroads were first being put into operation. It is there- fore possible that it really existed in America prior to that time, and that lack of facilities for its rapid spread prevented it from assuming the proportions of an epizootic. It is true that as early as 1822 an epizootic dis- ease resembling hog cholera was reported in 2. ; , < HOG CHOLERA France, and there is evidence that prior to 1833 outbreaks of a similar nature occurred in other parts of continental Europe. But even with pres- ent-day knowledge hog cholera and other infec- tious swine diseases are sometimes difficult to differentiate, and we are thus in the dark relative to the true causes of all the earlier outbreaks. According to the most authentic records, hog cholera appeared in England in 1862, and from there, in 1887, it was carried to Sweden in a ship- ment of boars. In this same year the disease ap- peared in France and Denmark, and its spread was so rapid and persistent that all European countries have suffered severely from its ravages. To-day, no large area devoted extensively to swine raising is entirely free from hog cholera, and so far as we have been able to ascertain, no country, once invaded, has succeeded in freeing itself of the malady. The Scandinavian countries seem to have suffered least from its effects. Because of its rapid spread and high mor- tality hog cholera has caused and is causing enor- mous losses, the estimate being that in the United States it is responsible for ninety per cent of the deaths from all swine diseases. In this country the annual losses caused by it during the last four decades have ranged between $13,000,000 and $200,000,000, and in the two decades ending with the year 1914 the average annual loss per one HISTORY AND ECONOMIC IMPORTANCE 6 thousand hogs has been approximately 66. In 1897, the loss per thousand ran as high as 130. Since 1914, the losses due to the disease have been gradually diminishing, and it is believed that more effective sanitary measures and more extensive and judicious use of protective serum have been responsible for this decline. Naturally a disease of such great economic im- portance has been the object of close and pro- longed study. In 1875, Dr. James Law furnished the United States Department of Agriculture with a report setting forth accurately the symptoms and lesions of the disease, and speaking for its transmissibility. Three years later, as a member of a commission of nine men appointed by the De- partment to investigate the disease, he succeeded in transmitting it by inoculation experiments. Dr. Detmers, acting as a member of the same commis- sion, isolated an organism which he regarded as its cause, but his findings were not confirmed. In 1885, Dr. Daniel Elmer Salmon and Dr. Theo- bald Smith isolated an organism, now known as B. suipestifer, which they believed to be the true cause of hog cholera. Their work was confirmed by trained investigators in this country and Eu- rope, but all attempts to produce immunity to field outbreaks by using B. suipestifer as an im- munizing agent ended in failure. Thus during the late nineties considerable doubt had developed 4 HOG CHOLERA among some scientists relative to the true signifi- cance of this organism in its relation to epizootic hog cholera. This doubt was aroused because hogs that sickened as a result of injections of B. suipestifer cultures failed to transmit disease to checks, because those that survived injection with cultures of the organism were not immune when exposed in field outbreaks, and because these cul- tures did not always produce disease, while blood from hogs sick as a result of natural infection proved to be quite generally infectious. In 1903, de Schweinitz and Dorset of the United States Bureau of Animal Industry demonstrated that the true cause of epizootic hog cholera is a filterable virus, and this marked an epoch in th6 history of the disease. Proceeding in the light of this new knowledge, Dorset, Niles and McBryde succeeded, in 1908, in adapting to hog cholera the principles employed by Kolle and Turner, Nicolle and Adil-Bey in pro- ducing a protective serum against rinderpest, a disease of cattle caused by a filterable virus. The work of Dorset and his associates was con- firmed by numerous investigators, among whom were Uhlenhuth, Hutyra and Xylander, and the epochal field experiments conducted in this coun- try by Dr. Niles and described by him in the re- port of the United States Bureau of Animal In- dustry, 1908, fully established the great practical HISTORY AND ECONOMIC IMPORTANCE O usefulness of anti-hog-cholera serum in checking the inroads of hog cholera in the field. Since 1908, rapid advances have been made in providing for an adequate supply of serum, in refining it, in working out methods for its use in the field, and in regulating its production so as to prevent sale of that which is contaminated or im- potent. All important hog-raising states in the Union have made provision to manufacture serum, and scores of private laboratories which have been established are being operated under super- vision of the Bureau of Animal Industry. In the refinement of the serum the aim has been to pro- duce, at low cost, a clear, sterile, potent product with good keeping qualities. This ideal is rapidly being attained, but there are still serious questions regarding uniform potency and keeping qualities of the clear serum, and the equipment required in making it is rather crude, and cannot be said to have passed the developmental stage. Finally, it should be related that with the knowledge that hog cholera can be controlled, there has appeared a quickened interest in all other maladies that affect swine, especially those frequently complicated with hog cholera. Undue importance has sometimes been attached to some of these diseases, and such extravagant claims have been made for certain biologies used as pro- phylactic or therapeutic agents that there has 6 HOG CHOLEKA been a sharp reaction, and there are indications at present that the trend of opinion may even swing too far in the opposite direction. The dis- eases that complicate hog cholera present very real problems, and experimental work looking to- ward a deeper understanding of them is one of the immediate needs of the present day. CHAPTER II NATURE AND CAUSE OF HOG CHOLEBA HOG cholera is an acute, communicable, febrile disease which attacks swine of all breeds and ages, but does not affect other domesticated animals, or man. It is a septicemia. Occasionally a per- acute form of the disease is recognized during the first days of an outbreak and chronic hog cholera is frequently observed among the stragglers that survive the more severe and rapidly terminating forms. In the individual, the disease is charac- terized by sudden onset, inappetence, chilling^ very high fever, arched back, a disposition to hide in the litter, constipation followed by diarrhea, general weakness in the later stages, accompanied by purplish discolorations of the skin covering the belly, ears and snout. In the herd, the onset is relatively slow, the first death usually preceding subsequent ones several days, but after the first week the outbreak rapidly gains momentum, and in a comparatively short time all hogs become in- fected. The mortality ranges between 80 and 100 per cent with a strong tendency to approach the latter figure. 8 HOG CHOLEBA Young pigs, especially those farrowed and nursed by immune mothers, are often immune to cholera during the first few weeks of life, and a general impression that all pigs nursing immune sows are likewise immune seems to have gained ground. This impression is not in accord with the facts, for we have seen individual pigs born of immune mothers and suckled by them, dead of hog cholera on the seventh day following birth, and under like conditions of birth and sustenance we have frequently seen entire litters succumb to the disease before attaining an age of four weeks. Among older hogs raised in localities where hog cholera is not prevalent, the " natural immunes" so frequently mentioned are by no means common, and it is probable that in places where they are found in considerable numbers they owe their im- munity to the fact that they are exposed to cholera as young pigs, and suffering only a slight reac- tion, are rendered immune. As a general rule, young shoats, old hogs, and sucking pigs are most susceptible to cholera in the order named, and, as would be expected, recoveries from the disease are less frequent among young shoats, and more frequent among old sows and sucking pigs. The cause of hog cholera is a filterable virus, probably an organism too small to be visible with the highest magnification now obtainable, and pos- sibly possessed of characteristics which prevent it STATUBE AND CAUSE OF HOG CHOLEEA from taking stains that render bacteria more plainly visible. The virus readily passes porce- lain and infusorial earth filters which retain all visible bacteria, but it is itself retained by the finest porcelain filters. It does not pass through colloid membranes. In the human subject, mea- sles, mumps, scarlet fever and smallpox are among the diseases caused by filterable viruses, while among animals rinderpest, foot-and-mouth dis- ease and rabies are some of the diseases that fall in the same group. The classification is a rather loose one, being based entirely on the fact that these viruses will pass filters that retain visible bacteria, rather than on morphological or cultural characteristics. There is no conclusive evidence that hog cholera virus has been propagated outside the bodies of infected swine. After a hog has been exposed to the disease and actually infected, the virus ap- pears in the blood stream in about four days, and thus all vascular organs harbor it during the at- tack. In the later stages of a few chronic cases, we have found the blood free of the virus, but we do not know whether this is the rule, nor is there definite knowledge of the part played by " car- riers " in harboring it. It is eliminated through the excretions. The urine is regularly infectious, the feces may or may not contain it, and the dis- charge from the eyes and skin ulcers is infectious 10 HOG CHOLERA at least in some instances. Just how any one of the filterable viruses operates to produce disease is quite unknown, but it is certain that hog cholera virus has a selective action for epithelial and en- dothelial cells. Virulence. Hog cholera virus produces speci- fic disease only in swine, and very small quantities of infected material are sufficient to cause death in susceptible animals. According to King, sub- cutaneous injections of 1/86 of a mil of virulent blood produced the disease, while lesser amounts produced only a mild reaction, or none at all. Natural infection usually occurs by way of the digestive system, but the disease is readily pro- duced by subcutaneous, intravenous or intra-abdo- minal injections of small quantities of virulent material. Resistance. Most of the natural influences to which hog cholera virus is subjected do not oper- ate to destroy it rapidly. Drying, sunlight, and low temperatures seem to have no immediate at- tenuating effects, although it is a fact that most infected yards which remain uninhabited from three to six months do not endanger susceptible pigs placed in them. There is, though, a consid- erable tendency for hog cholera to recur on old infected farms, and this fact indicates that there are exceptional cases in which the span of life of the virus is greatly prolonged. NATURE AND CAUSE OF HOG CHOLERA 11 Putrefaction is the only natural influence which operates to destroy the virus rapidly. Ac- cording to Uhlenhuth it will live in putrefying car- casses for about eight days, but undoubtedly the many influences which govern putrefactive proc- esses render data of this kind of value merely in establishing tendencies. It is certain that decom- posing carcasses do not harbor the virus regu- larly, and likewise it is true that virus kept in bot- tles in the laboratory often is killed when putre- faction develops. When sufficient preservative is added to prevent the growth of putrefactive or- ganisms, the virus regularly lives several months, and may even exist for years. Moderate degrees of heat attenuate or destroy the virus, and under no circumstances has it been found to survive temperatures near the boiling point. The following rather incomplete table pre- pared by the German Imperial Board of Health laboratories gives a fair idea of the effects pro- duced by various degrees of heat. Degrees Material Centigrade Time Results Liquid serum filtrate 45 24 hours Not killed or weakened Liquid serum filtrate 46.5 24 hours Not killed or weakened 12 HOG CHOLEEA Degrees Material Centigrade Liquid serum filtrate 46 Liquid serum filtrate 55 Liquid serum filtrate 60 Liquid serum filtrate 58 Liquid serum filtrate Dried blood Dried blood Dried blood Urine Urine 78 65 72 72 58 58 Time Results 48 hours Killed 24 hours Killed 10 hours Killed 2 hours Not killed 1 hour 2 hours 1 hour !/2 hour 1 hour % hour Killed Not killed Killed Killed Killed Not killed Low temperatures act to prevent growth of putrefactive organisms and are thus instrumental in prolonging the life of the virus. In our own experiments, hams removed from cholera infected pigs and frozen hard ninety-three days still har- bored virus sufficient to produce the disease when small portions of them were fed to susceptible pigs. Disinfectants. Hog cholera virus readily re- sists ordinary disinfectants in dilutions that are rapidly fatal to most bacteria. When y2 per cent phenol is added to virulent blood, the virus will remain alive for months, and all of the coal tar disinfectants must be prepared in strong solutions in order to destroy it. Liquor cresolis compositus NATURE AND CAUSE OF HOG CHOLERA 13 in 5 per cent aqueous solution, when allowed to act for an hour or more, has proved effective in killing it. Following is a table prepared by the German Imperial Board of Health laboratories, which fur- nishes additional information relative to the effec- tiveness of various disinfectants when used to kill hog cholera virus. Most of the tests were made by mixing 10 mils of the virus with an equal quantity of aqueous dilution of the disinfectant. Dilution applied Disinfectant Corrosive sublimate Corrosive sublimate Corrosive sublimate Carbolic acid Carbolic acid Carbolic acid Carbolic acid 0.3 per cent solution 0.5 per cent solution Result Serum filtrate not killed in 8 days. Serum filtrate virus not killed in 4 days. 0.2 per cent solution Urine virus killed in 15 minutes in one trial. In another trial not killed. 0.5 per cent solution Serum filtrate virus not killed in 8 days. 1.0 per cent solution Serum filtrate virus not killed in 4 days. 3.0 per cent solution Failed to kill blood virus in 8 days. 2.5 per cent solution Failed to kill urine virus in 15 minutes. 14 HOG CHOLEBA Dilution Disinfectant applied Chloroform Full strength Sodium taurocholate Formaldehyd 2.5 per cent solution Lugol 's solution 0.25 per cent solution Urea 20.0 per cent solution Glycerin 33.0 per cent solution Ozone Hydrogen peroxid 10.0 per cent solution Antiformin 5.0 per cent solution Antiformin 2.0 per cent solution Result Serum filtrate virus not killed in 24 hours. Blood virus not killed in 4 days. Serum filtrate virus alive after one hour. Dead in 15 days. Failed to kill serum filtrate virus in 2 hours. Did not kill serum filtrate virus in 1 month. Failed to kill serum filtrate virus in 1 month. Blood virus not killed. Serum virus not killed in two hours. Serum filtrate virus killed in one hour. Urine virus not killed in 10 minutes. Killed in 15 min- utes. Antiformin 1.0 per cent solution Serum filtrate virus not killed in 24 hours. NATURE AND CAUSE OF HOG CHOLERA 15 Disinfectant Antiformin Milk of lime Chlorid of lime Lysol Dilution applied Result 2.5 per cent solution Serum filtrate virus killed in 2 hours. Blood virus not killed in two hours. Failed to kill in one hour. In other ex- periments killed in 20 min. 5.0 per cent solution Serum virus killed in 1% hours. 3.0 per cent solution Serum filtrate virus usually killed in 1 hour. Cresol soap solution 3 — 6 per cent solution Always killed virus in 1 hour. Cresol soap solution 3 — 4: per cent solution Serum filtrate virus not killed in % hour. Cresol soap solution 3.0 per cent solution Killed urine virus in y^ hour. Since a filterable virus has been incriminated as the true cause of hog cholera, various investiga- tors have from time to time attempted to isolate it, stain it, and grow it on artificial culture media. King has made an exceedingly careful study of a spirochaete (Spirochaeta hyos) which to him has seemed to possess etiological significance, but his 16 HOG CHOLEEA work has never been verified. More recently Proescher and Sell have described a diplococcus which they are inclined to regard as the virus of hog cholera, but as yet they have not submitted substantial proof to justify such a claim. Certain cell inclusions which in cholera-infected hogs ap- pear in the epithelial cells of the conjunctival sac have also been regarded as possible possessors of pathogenic powers, but it now seems probable that these exist as an effect rather than as a cause. There are various organisms which, acting as secondary invaders, exert profound influence on the course of hog cholera and on the lesions which develop, but which should in no way be confused with the filterable virus that produces the dis- ease. These will be considered in another chap- ter. CHAPTER III METHODS OF DISSEMINATION HOG cholera virus exists only in infected hogs and in material contaminated by their excretions, and this is the fundamental fact to which we must repeatedly refer in accounting for new outbreaks. There are numerous exceptions to the rule, but the individual outbreak can usually be traced to a definite source, and this fact is important in its relation to measures for control. Shipping infected animals is probably the one practice responsible for most new herd infections. It is not uncommon for a breeder to become dis- couraged when his hogs begin to die and to ship all seemingly well animals to a distant market. During the fall of the year especially one has but to stand for a few hours at the unloading chutes of some of our large stockyards in order to realize how nearly universal this practice has become. Thus most public stockyards harbor hog cholera virus, and all hogs unloaded in them and later taken to farms for feeding or breeding become potential sources of danger. In the eastern states garbage feeding is re- sponsible for more outbreaks of hog cholera than 17 18 HOG CHOLERA all other factors combined, and in the country as a whole this practice plays an exceedingly im- portant part in the spread of the virus from local- ity to locality. Many hogs are killed while they are in the incubation period of cholera, and pork that comes from their carcasses, even though it is fit for human food, will produce hog cholera when fed in small portions to hogs. Bits of this in- fected pork find their way into garbage which is fed to susceptible swine, and the cycle is com- plete. The use of hog cholera virus in the field in serum-virus immunization has now become a rou- tine measure, and despite the advantages that re- sult from this practice, it must in truth be said that it is responsible for many new outbreaks of hog cholera. The practice of giving feeding shoats serum-virus treatment and shipping them immediately to distant points operates to infect much new territory, and is often the cause of heavy losses among the hogs thus handled. "Vaccination cholera," as these " breaks " follow- ing serum-virus treatment are called, although it usually runs a less rapid course which invites sec- ondary infection, is not fundamentally different from hog cholera contracted as a result of natural infection, but there is a marked tendency in some quarters to avoid the issue and attribute the deaths to causes other than hog cholera virus. METHODS OF DISSEMINATION 19 The practice of taking breeding hogs to dis- tant points to mate them is a fruitful source of new herd infections, and in more than one instance we have known the virus to be carried from one farm to another as a result of neighbors exchang- ing help during butchering time. Small streams to which many hogs have access may also become polluted and carry destruction to herds below the one in which the original infection occurs. Show hogs returned from fairs often contract hog chol- era en route or during their contact with other hogs in the show ring, only to infect the herds they represent when they return home. Besides the regular channels of infection which we have already indicated, and which severally are responsible for most new outbreaks of hog cholera, there are almost an infinite number of casual carriers of the virus, such as crows, spar- rows, buzzards, pigeons, and various predatory animals. These, by feeding in infected yards or on carcasses of hogs dead of cholera, may carry the infection to clean territory, but the probabili- ties are that in most localities the number of herds thus infected is relatively small. In recent experiments Dr. Marion Dorset has found it difficult to transmit hog cholera from herd to herd by employing attendants, pigeons and sparrows as agents of transmission, and in our own experiments we have failed in a surpris- 20 HOG CHOLEEA ing percentage of cases to infect yards with hogs sick of cholera so that susceptibles placed in them subsequently will contract the disease. In spite of these facts, though, we must in handling hog cholera be guided by the practically universal clinical experience which teaches that when hog cholera once finds its way into a farm herd it will eventually infect all individuals in it, irrespective of the fact that the herd may consist of several pens of hogs kept some distance apart. It is impossible, and indeed unnecessary, to dis- cuss in detail the various influences which occa- sionally are instrumental in carrying hog cholera virus from herd to herd, and likewise it is impos- sible to assign to each influence a relative import- ance. It is much more important, in concluding this chapter, to call attention again to the fact that in the great majority of cases hog cholera virus travels in certain quite definite channels, and that new outbreaks are usually the direct or in- direct result of shipping or moving infected hogs, or else they originate from the practice of garbage feeding, or that of using hog cholera virus indis- criminately in seeking to immunize against the disease. CHAPTER IV COMPLICATIONS BEFORE we consider the symptoms, lesions and diagnosis of hog cholera, it is necessary that we shall discuss briefly some of the organisms that complicate the disease, and which at times exert such profound influence on its course that autop- sies become a continual source of surprise and perplexity to the diagnostician. No attempt will be made to give complete morphological and cul- tural characteristics of these organisms, which in- formation may be found in various standard works on bacteriology. The scope and purpose of this book require that we shall deal only in a general way with most biological characteristics, confining our attention chiefly to disease produc- ing power, especially in swine. Bact. suisepticum is the most important of the organisms that complicate hog cholera. It was isolated and described by Loeffler and Schiitz in 1885, and in 1886 Dr. Theobald Smith recovered it from various organs of many hogs dead of an epizootic disease in this country. Moore showed that it is present in the upper air passages of 21 22 HOG CHOLEBA many healthy swine. In the absence of knowledge of the filterable hog cholera virus, all these investi- gators were inclined to regard the organism as the cause of epizootic swine plague, and to ascribe repeated failures in causing it to produce trans- missible disease, to the fact that field conditions could not be duplicated in the laboratory. The organism is rod-shaped varying in length from .8 to 2 microns, and in width from .4 to 1.2 microns. Often the ends are rounded giving it an oval shape, but it is not uncommon for the rods to be so short as to resemble micrococci. Some- times involution forms are observed. In cover- glass preparations made direct from the tissues and stained with basic aniline dyes, Bact. suisepti- cum often stains heavily at the ends and around the periphery, and very lightly or not at all in the center. Preparations made from cultures do not as a rule exhibit this bipolar staining. The organism is subject to wide variation in virulence. Babbits, mice and guinea-pigs readily succumb to injections of minute quantities of cul- tures or suspensions containing it. Babbits are especially susceptible, usually dying in less than thirty-six hours of an acute bacteremia. Like cul- tures or suspensions injected subcutaneously into cholera immune pigs produce as a rule a transient local reaction. Small doses injected intravenously may or may not prove fatal, but large intrave- COMPLICATIONS 23 nous doses produce death from septicemia quite regularly. The pigs that die in less than seventy- two hours may show as lesions congestion of the lymph glands and various parenchymatous or- gans, or, more rarely, petechial hemorrhages in the kidneys and heart, indistinguishable from those observed in acute hog cholera. In the cases in which the disease runs a less rapid course, there is a rather constant tendency for joint lesions of an inflammatory nature to form, and, contrary to what might be expected, pleuritis and pneumonia appear much less frequently than these joint le- sions. Rarely do checks kept with these experi- mental animals contract disease.1 The symptoms that appear in pigs artificially infected with large intravenous doses of Bact. suisepticum are observed in a very few hours after the injection. There is rapid breathing, sometimes an extreme degree of dyspnea, or the respiratory disturbance may manifest itself in 1 ' thumping. ' ' The appetite is suspended, the tem- perature is moderately high (104°-105.5° F.) and there is an anxious facial expression. A general stiffness is practically always observed, and *In our own experiments, in which more than 100 pigs were exposed in pens with pigs artificially infected with intravenous injections of Bact. suisepticum, 3 contracted disease and 2 died. Bact. suisepticum was recovered from the blood and various parenchymatous organs of the dead animals. We know of no other well authenticated instances in which like transmission has occurred. 24 HOG CHOLEEA lachrymation often is pronounced. If death or recovery does not take place in two or three days, the tendency is for the disease to assume a chronic type. One or more of the joints, usually the knee or hock, becomes hot, painful, and swollen, render- ing it difficult or impossible for the animal to stand. In spite of this, the temperature falls and is maintained close to normal, the appetite returns and is surprisingly good considering the condition of the animal and the fact that progressive ema- ciation is taking place. Pneumonia sometimes appears in these chronic cases, adding its train of symptoms, but it fails to develop in a surprising percentage -of cases, thus presenting a striking comparison with field outbreaks formerly thought to be caused solely by Bact. suisepticum, in which pneumonia is the most constant manifesta- tion. These facts lead us to doubt that the or- ganism, acting alone, is the cause of a rapidly transmissible disease in the field. Field observations are in almost perfect accord with these experimental data. We have frequently had outbreaks of "pure swine plague " reported to us, and in those we have investigated, in which there was evidence of transmissible disease, we have without exception succeeded in positively demonstrating or establishing the probable pres- ence of the filterable hog cholera virus. It is also significant that in the East, at least, cholera im- COMPLICATIONS 25 mune hogs do not suffer from " swine plague " if we except the cases in which it is said to appear in the first month subsequent to serum-virus treat- ment, and which in reality have their origin in the hog cholera virus used. Acting as a secondary invader in hogs suffering with cholera, in those badly infested with lung worms, and very probably as a primary microbian cause in those weakened as a result of shipping, Bact. suisepticum regularly produces a rather characteristic bronchopneumonia, and hastens or causes death. In those cases in which it acts as a secondary invader it produces pneumonia so rap- idly and regularly that the lesions due to the pri- mary cause are often obscured or overlooked. Cholera immune farm hogs kept in exceedingly bad sanitary surroundings and exposed regularly to damp and inclement weather, have not been shown to suffer from a rapidly transmissible and fatal pneumonia caused by this organism. There is, though, some experimental evidence that it oc- casionally produces pleuritis or possibly slight pneumonic lesions from which most hogs recover. B. suipestifer (B. cholera suis) is another or- ganism which may often be isolated from various parenchymatous organs of hogs dead in outbreaks of cholera. It is a short, motile rod, belonging to the colon group. In 1885 it was described by Salmon and Smith as the cause of epizootic hog 26 HOG C^EOLEKA cholera. In later years Uhlenhuth and his co- workers reported finding it in the intestinal tracts of many healthy swine. Jordon, in this country, was unable to identify it in any normal hogs which he examined, and neither was Tenbroeck. Both of these investigators regard Uhlenhuth 's work as inconclusive owing to the fact that he did not differentiate correctly between B. suipestifer and B. paratyphoid B. Smith states that the only dis- tinction that can be made between the two is that the former is pathogenic for rabbits, while the latter is not. Eabbits and guinea-pigs succumb to small sub- cutaneous injections of cultures of B. suipestifer, rabbits being somewhat more susceptible. Swine are not easily infected with subcutaneous injec- tions, but large intravenous doses prove fatal. According to Welch, small doses may lead to for- mation of the "button ulcers" observed in chronic hog cholera, and Smith secured like results by feeding pigs bouillon cultures. The part played by this organism in producing swine disease in the field is not well defined, as most work with it ceased as soon as the filterable virus was accepted as the cause of epizootic hog cholera. There is good evidence that it is one cause of the "button ulcers " just mentioned, and it is likewise probable that, acting in the role of secondary invader, it is responsible for the en- COMPLICATIONS 27 larged, dark, and somewhat pulpy spleens ob- served in individual hogs dead in outbreaks of cholera. It also seems to intensify hemorrhagic lesions produced by the filterable virus. Its pathogenic powers in relation to cholera immune pigs will bear further investigation, but it is prob- able that for the most part it acts to complicate diseases produced by other causes. B. pyocyaneus, or, according to Migula's classi- fication, Pseudomonas pyocyaneus, is a motile rod 2 to 6 microns long and .3 to 1 micron broad. It is widely distributed in nature, and there has been a tendency to regard it chiefly as a saprophyte. It is included frequently in the flora of wounds, it appears at times in abscesses in swine and other animals, and it has been described as the cause of an outbreak of dysentery in man. In Germany it is said to be the cause of an infectious nasal catarrh in pigs, and we have found it associated with outbreaks of pneumonia in swine, as the prob- able cause. The organism is an aerobe, it grows luxuriantly on the common culture media, tending to over- whelm other bacteria associated with it. It has a marked tendency to produce green color in any cul- ture medium, and the sweetish odor produced by it in bouillon cultures is quite characteristic. It takes the aniline stains regularly, and is Gram negative. 28 HOG CHOLERA B. pyocyaneus is pathogenic for pigeons, guinea pigs and rabbits. In swine, it is not regularly so, but under certain conditions it assumes great pathogenic significance. We have failed to pro- duce disease by feeding cultures of it or by spray- ing them into the nostrils of healthy pigs, while subcutaneous doses produced nothing more than an occasional local abscess. Moderate intrave- nous doses of suspensions containing it cause dyspnea, chilling or spasms to appear immedi- ately, and death, preceded by paralysis, usually of the hind quarters, often takes place in a day or two. This paralysis is observed in rabbits as well, and must be regarded as a more or less constant but nevertheless specific action on the part of the organism. According to Hutyra, cultures of B. pyocyaneus inoculated directly into the ethmoid mucosa in young pigs, produce disease similar to the catarrhal rhinitis observed in Germany. Under natural conditions certain predisposing factors, among which early age, lung worms, hog cholera virus and long confinement in very dusty quarters are most important, prepare the ground so that B. pyocyaneus exerts its pathogenic pow- ers. We have observed its effects following hyperimmunization during the process of anti-hog- cholera serum preparation, the hypers developing a fatal pneumonia in a few days following a large intravenous dose of hog cholera virus. COMPLICATIONS 29 The lesions produced in swine experimentally infected by means of intravenous injections of material containing B. pyocyaneus are those char- acteristic of septicemia, congestion and dark col- oration of the lymph glands, lungs, kidneys and other organs appearing regularly. We have ob- served no such effects where natural infection rules. Here the constant lesion produced is pneu- monia, acute or chronic, and the constant symp- toms that appear are those that may be referred to this condition. Dyspnea, abdominal breathing and other marked evidence of respiratory distress charac- terize the disease. Paroxysms of coughing occur when the hog is required to move, the alae of the nostrils are drawn backward, giving the snout a peculiar pointed appearance, and it is not uncom- mon for the affected animals to assume a dog- sitting position, with the forelegs placed widely apart. Thumping appears frequently. Some- times there is a yellowish purulent discharge from the nostrils. The appetite may or may not be affected, while the temperature, as a rule, remains normal or is only slightly elevated. The typical lesion which we have found associ- ated with natural infection due to B. pyocyaneus consists of a semi-chronic type of bronchopneu- monia, affecting first the ventral and cephalic portions of the lungs, or if lung worms are pres- 30 HOG CHOLERA ent, the posterior border of the diaphragmatic lobe as well. The solidified portions may be red but are often rather light in color, macroscopically resembling the surface of a salivary gland. There is a marked tendency for necrosis to develop from numerous foci, and multiple abscesses occur, appearing as slightly elevated yellow areas dotted over the surface of the pneumonic lung. Pleuritis is somewhat constant, and a high degree of em- physema appears in the dorsal nonpneumonic por- tion, giving it a pale white color as compared to the normal pink. Often there is distinct evidence that as a final cause of death an acute pneumonia is superimposed over a more chronic type, in which cases all parts of the lungs are pneumonic, while the lesions in the dorsal and posterior por- tions are of more recent origin. B. necrophorus is another organism that some- times complicates hog cholera. Although subject to wide variations in form, it usually appears as a long, slender, nonmotile rod. It is a strict anaer- obe, it stains with the ordinary aniline .dyes, and is Gram negative. Evidently it is quite widely distributed in nature, for it appears in numerous necrotic lesions in practically all domesticated ani- mals. It is regarded as a normal inhabitant of the intestinal tract in swine, and it exists in soil con- taminated with manure. It is the exciting cause of calf diphtheria, lip and leg ulceration in sheep, COMPLICATIONS 31 and a necrotic stomatitis of calves and pigs, each of which partakes somewhat of the nature of a specific infectious disease, but none of which, with the possible exception of calf diphtheria, tends to be reproduced regularly, in typical form, by arti- ficial means. In swine, B. necrophorus may be the primary, and usually is the exciting cause of various ne- croses which appear in the mouth, stomach and intestines, nasal passages, skin, and lungs, and are designated, respectively, according to loca- tion, necrotic stomatitis, enteritis, rhinitis (bull nose), dermatitis and pulmonary bacillosis. The typical lesion consists of a dark brown necrotic patch which spreads slowly and tends to penetrate the deeper structures. Frequently a yellowish- brown scab or false membrane is formed. In ne- crotic stomatitis and enteritis especially, numer- ous lesions often coalesce until large areas are af- fected, and, depending on location, even the man- dible itself may be involved or the intestinal wall penetrated. A foul odor is usually detected. In the mouth, the lesions usually take origin from teething wounds or other slight abrasions ; in the stomach and intestines, hog cholera lesions and various irritants prepare the ground for their development; in the nasal passages they follow rhinitis due to other causes ; in the skin, they ap- pear especially on the teats and udders of sows 32 HOG CHOLERA which are chapped or wounded as a result of nurs- ing litters. We know less regarding the primary cause of necrotic lesions that appear in the lungs. It is still an open question whether B. necropho- rus is really capable of penetrating normal mu- cous membrane and producing its characteristic effects, but usually it does not. Likewise there is doubt as to whether it releases a toxin, the prob- ability being that at times it does, for especially in young pigs suffering with necrotic stomatitis, death often takes place suddenly, before it can be explained on the basis of the existing local lesion. On the other hand, some pigs will harbor surpris- ingly extensive lesions without marked systemic disturbances. Some regard B. necrophorus as a secondary invader that may cause the "button ulcers " which appear in chronic hog cholera, but there is at least a distinct difference between the button ulcer in which degenerative and regenera- tive processes coexist, and the usual lesion pro- duced by B. necrophorus, in which a progressive necrosis prevails as long as the exciting cause re- mains active. There is also somewhat meager evidence that the organism may in rare instances cause petechial hemorrhages in the serous mem- branes and kidneys. Bact. suisepticum, B. suipestifer, B. pyocya- neus, and Bact. necrophorus have two characteris- COMPLICATIONS 33 tics in common. All are of a subvirulent nature, usually depending on other influences or predis- posing causes to enable them to exert their patho- genic powers, and all frequently take advantage of the lesions produced by hog cholera virus, in which they establish themselves, changing the course of the disease, and rendering autopsies puzzling and inconclusive. There are several other organisms that have been associated with hog cholera, either as com- plicating influences or probable causes, but some of these normally lead a saprophytic existence, and with our present knowledge we are unable to assign to any one of them a definite pathogenic role. B. coll communis and other members of the group, together with various streptococci and micrococci may often be found in lungs of hogs that have died of a terminal pneumonia brought on by hog cholera. Spirochceta lnyos (King) is sometimes found in the blood and intestinal le- sions of hogs suffering with cholera, and B. py- ogenes suis is found in various suppurating lesions in swine, some of which have died in hog cholera outbreaks. The collective primary and secondary effects of all the organisms considered in this chapter, together with the changes produced by hog cholera virus go to make up the symptom- complex which, conveniently but unfortunately, has come to be known as " mixed infection, " and 34 HOG CHOLERA handled as a single entity. Only when we begin to inquire more closely into the disease-producing powers of each organism will real progress be made. CHAPTER V SYMPTOMS AND LESIONS FOLLOWING the subcutaneous injection of a small quantity of hog cholera virus, or the feeding of material containing it, symptoms of the disease usually appear between the fifth and eighth days. In herds through which the disease is spreading, several weeks are often required for it to reach all individuals, but this delay must be regarded as due to failure of some of the hogs to take up the virus, rather than as a prolonged incubation period. The incubation period usually given va- ries between four and twenty-one days, but in the vast majority of cases symptoms will appear in less than nine days following definite exposure (feeding or inoculation) of susceptible pigs. Three forms of hog cholera are recognized, per- acute, acute and chronic. The peracute form is relatively infrequent, but it occurs occasionally among the first few hogs that succumb in an out- break. No definite symptoms have been asso- ciated with this form of the disease, for the af- fected animals are found dead with no history of previous sickness. 35 36 HOG CHOLERA The acute form, which includes the great ma- jority of cases, begins with high fever (105°-109° F.), arched back, chilling, rough coat, drooping ears and tail, and general depression. The appe- tite is impaired. The affected animals may crowd to the trough in the usual greedy fashion, but after drinking sparingly of any liquid that may be contained in the feed, they return languidly to the nest in advance of their associates, slowly draw the litter backward with alternating fore- feet, and then settle to sternal recumbency with the snout hidden beneath the litter, seemingly in an effort to keep warm. Intermittent attacks of chilling shake the body, the reflexes are dulled, the eyes closed, and a general stupor prevails. Conjunctivitis, mild or severe, is practically al- ways present, causing an exudate of a seromucous or seropurulent type to appear, gumming the eye- lids together, or forming crusts which remain in the internal canthus and on the margins of the lids. Early in the attack, constipation is noted. The fecal balls, usually dark in color and often cov- ered with mucus, are voided with difficulty. Later, if death does not ensue, diarrhea sets in, and continues pending the advent of death or con- valescence. The character of the food determines the color of the feces. As the sick hog lies undisturbed in the nest 37 38 HOG CHOLERA there is often noted a scarcely audible, high- pitched, complaining expiratory grunt, but if the animal is seized suddenly it struggles feebly and emits a weak, hoarse squeal. The gait may be unchanged, but often staggering is noticed, and sometimes there is a characteristic unsteadiness or weaving in the hind quarters, best observed in well advanced cases when the animals are caused to move without undue excitement. Convulsions appear somewhat infrequently, and may be regarded as the only violent hog cholera symptom. The attack usually occurs at feeding time or under stress of other excitement, more often in young pigs. The pig comes to the trough as if to eat, but suddenly backs away, squealing, with the snout drawn low between the forelegs. The muscles stiffen in spasm, the pig falls on its side, the eyeballs roll upward, the legs are in con- stant motion, and the snout is gradually extended with a jerky, convulsive movement. The attack lasts less than a minute and terminates either in death or complete return of nervous function. Early in an attack of hog cholera, the skin is flushed, hot and sensitive, the flush being appar- ent only in clean white pigs. Later, as death ap- proaches, a diffuse purplish discoloration some- times appears in the skin covering the ears, snout, belly and inner surfaces of the legs, and is less frequently observed at the extremity of the tail, SYMPTOMS AND LESIONS 39 on the vulva, and in the perineal region. Depend- ing on whether the color results from hyperemia or hemorrhage, it will or will not disappear on pressure. Sometimes congestion and hemorrhage coexist, in which case the color disappears for the most part, revealing the presence of ecchymoses in the pressure-whitened area. Less frequently ecchymoses exist alone. Somewhat infrequently skin ulcers appear on the throat and between the forelegs, very rarely elsewhere on the body. They are light brown, irregularly round or oval in shape, %-2 centimeters in diameter, and cov- ered with scabs. A rusty yellow, very sticky exu- date, most apparent on the ventral scantily-haired body surfaces, is noted in some individuals. Cough is observed in many field outbreaks, but it is by no means a constant symptom in uncom- plicated hog cholera. We have failed to establish a definite relation between this symptom and the petechial hemorrhages which appear in the laryn- geal mucosa. Respiratory symptoms are not prominent in hog cholera unless it is complicated with pneumonia, but dyspnea develops frequently under forced exertion. The superficial inguinal lymph glands are fre- quently enlarged so as to attract attention, and another common symptom is the collection of urine in the sheath of the male pig, causing marked dis- tention. When pressed out manually, the urine 40 HOG CHOLERA has a very offensive odor, and may be cloudy white in appearance, or otherwise abnormal. As the disease progresses, emaciation is quite rapid, and general weakness prevails. Frequently a terminal pneumonia develops during the last few hours, and death may result from heart or respiratory failure. Chronic hog cholera occurs, for the most part, among stragglers that survive the acute form, but it may exist independently among semisusceptible young pigs. Emaciation, cough, depraved appe- tite, diarrhea, unsteady gait, drooping ears and tail, tucked-up flank, and even sloughing of the skin are among the symptoms that appear. Some animals recover, but complete return to normal health is not the rule. LESIONS Peracute hog cholera does not usually produce characteristic macroscopic lesions, but congestion of the lymph glands, mesenteric vessels and var- ious parenchymatous organs may often be ob- served. It is in the acute uncomplicated form that the most typical lesions occur. These con- sist of congestion, hemorrhages and degeneration, hemorrhages being the only ones which, by virtue of character or location, are highly characteristic of the disease. These appear as petechiae in the kidneys, serosa of the intestines, mucosae of the SYMPTOMS AND LESIONS 41 bladder and larynx, in the pericardium, epicar- dium, and on the auricles of the heart, especially the left. Exceptionally they are seen in the dia- phragm, in the parietal pleura and peritoneum, and subjacent connective tissue. In the lungs, the hemorrhages usually appear beneath the pleura as ecchymoses, more often in the ventral portions of the cephalic and cardiac lobes, but at other times unconfined to particular areas. In the spleen they appear as well-defined slightly raised black areas % to 1% centimeters in diameter, practically always at the edge of the organ and visible beneath its capsule from the dorsal aspect. Some of the lymph glands are practically always congested or hemorrhagic. The hemorrhage ap- pears first around the periphery as the sectioned surface will show, later extending to the trabec- ulae, and finally in some cases progressing so far that the entire structure becomes infiltrated, show- ing on section a uniform dark color. Petechiae and ecchymoses in the lymph glands are excep- tional. The nodes most regularly involved in- clude the gastric, hepatic, lumbar, superficial in- guinal, mediastinal and submaxillary. The hemorrhages which are found in and be- neath the alimentary mucosa may appear in the form of petechiae or ecchymoses, but there is a marked tendency, due probably to constant me- chanical irritation, for them to become more 42 HOG CHOLEEA diffuse in character. The pharynx and esophagus are rarely affected, the stomach and small intes- tines frequently are, while the mucosa of the cecum and upper colon usually is involved. The skin lesions may consist of congestion or hemorrhage of circumscribed or diffuse nature, the latter type being by far the most common, and appearing as a purplish discoloration usually con- fined to the ears, belly, snout, inner surfaces of the legs, tip of tail, vulva, and perineal region. Small skin ulcers less than two centimeters in diameter, irregularly round or oval in shape, brown in color and scabbed over, appear somewhat infrequently on the throat, very exceptionally elsewhere on the body. These seemingly take origin from previous hemorrhages. Some have considered all these changes as due to secondary invasion, holding to the belief that hog cholera virus in itself does not produce mac- roscopic lesions. To this view we are unable to subscribe, for one may transport filtered virus hundreds of miles, and it will still produce, regu- larly, some or all of the leions just described, and it is inconceivable that the same secondary in- fluences should be present in all localities. In order to place in relief the more character- istic macroscopic lesions which, according to our conception, are due usually to unaided action of the filterable hog cholera virus, we have for the SYMPTOMS AND LESIONS 43 moment neglected discussion of less characteris- tic changes which frequently take place. If we consider each organ separately, extending our ob- servations to include less characteristic changes, as well as those produced by secondary invaders discussed in a previous chapter, a more complete picture, and a more accurate interpretation1 of the pathological anatomy encountered in field cases can be presented. Mouth and pharynx. Mucosa usually normal. Hog cholera virus may be primary cause of ulcers. These are sometimes present in hog cholera out- breaks, and appear as dark brown necrotic patches on gums, lips, tongue and other parts. Probably due to primary injuries caused by the filterable virus, and certainly caused by B. necrophorus as a secondary invader. B. necrophorus ulcers oc- cur independent of filterable virus infection. Stomach. Mucosa frequently normal. Filter- able virus causes petechise, ecchymoses or larger suffusions in fundus. Congestion due to the same cause usually present. Ulceration relatively rare, 1 We are fully aware that with our present knowledge such an interpretation can be only approximately correct, but nevertheless there are certain well-defined tendencies which should be indicated. Our conception of the primary filterable virus lesion has been gained, during the last ten years, by performing autopsies on hundreds of pigs which were killed about a week subsequent to injection with virus. The virus was obtained from several sources in various states, some was filtered, some was not. We have also investigated several of the secondary invaders, and the combined results of these investigations with those of similar nature con- ducted by other workers, are reflected in the remarks which follow. 44 HOG CHOLERA but necrotic patches due to secondary infection with Bact. necrophorus may appear. Serosa usu- ally normal. Exceptionally studded with puncti- form hemorrhages, due to filterable virus. Small intestine. Mucosa sometimes normal. Congestion rather common, also hemorrhages sim- ilar to those observed in stomach, and due to filter- able virus. Lymphoid nodules often congested, less frequently hemorrhagic, due to filterable vir- us. Those in ilium most frequently involved. Ulceration rather uncommon, except in extreme posterior portion of ileum. Serosa usually nor- mal. Petechial hemorrhages appear infrequently, mesentery often congested. Changes due to filter- able virus. Caecum and upper colon. Mucosa most con- stant seat of digestive canal lesions, especially region of iliocecal valve. Congestion, petechise, ecchymoses1 and larger suffusions common. Strong tendency toward ulceration. Pitlike patches denuded of epithelium. Necrotic ulcers or patches, dark brown in color, sometimes false membrane ; ulcers tending to broaden and deepen, little tendency toward regeneration. " Button ulcers ' ' 1 occur in chronic hog cholera. Serosa 1 The ulcers may be isolated and appear as circular, slightly projecting masses stained yellowish or blackish or both in alter- nate rings, or they may be slightly depressed and somewhat ragged in outline. When the superficial slough is scraped away many ulcers show a grayish or white base. A vertical section reveals a rather firm neoplastic growth, extending usually to the inner mus- SYMPTOMS AND LESIONS 45 often normal, petechiae not infrequent. Hemor- rhages and destruction of epithelial cells probably due to filterable virus. "Button ulcers " due to B. suipestifer, possibly to other organisms. Necrotic patches usually due to Bact. necro- phorus. Lower colon and rectum. Usually normal or nearly so. Sometimes congested. Infrequently the lower colon shows the same change as the upper colon. Larynx. Mucosa frequently normal. Some- times congested, more often dotted with petechiae caused by filterable virus. Trachea and bronchi. Mucosa often normal. Sometimes congested. Probably due to filterable virus. Lungs. Very often normal. Primary lesions sometimes caused by filterable virus consist of ecchymoses visible beneath the pleura. These ap- pear most frequently on the cephalic and cardiac lobes, but are not confined to these parts. Terminal pneumonia due to filterable virus plus nonspecific secondary invaders. Often affects all cular coat. When sections of such an ulcer are stained with aniline dyes and examined under the microscope, the submucous tissue is very much thickened, infiltrated with round cells and con- taining a large number of dilated blood vessels. Eesting upon this thickened submucosa, is a line of very deeply stained amor- phous matter, and upon this is situated the necrotic mass which fails to retain the coloring matter and which is permeated by a very large number of bacteria of various kinds. Frequently the eggs of trichocephalus are imbedded in the slough." — Moore, Pathology of Infectious Diseases. 46 HOG CHOLERA lung tissue. Lung solidified, red. Pneumonia of recent origin. Swine plague pneumonia due to filterable virus PLATE 2. Lung of pig showing ecchymoses due to acute hog cholera. These appear in greater numbers on the apical and cardiac lobes plus Bad. suisepticum. Cephalic and cardiac lobes first to be affected, later other parts may solidify. Solidified portion usually red or reddish gray. Usually bronchopneumonia. Interlobular SYMPTOMS AND LESIONS 47 spaces well defined macroscopically, due to infil- tration of leucocytes or blood. Tendency toward necrotic and caseous masses in cases of longer standing. Pleuritis constant. Pleurae often thickened, rough, white, adherent. Pneumonia, characterized by necroses which start from various foci, tending to involve all structures alike, sometimes spreading to the heart by contiguity. Filterable virus plus Bact. necro- phorus. Pneumonia, often semichronic, tending toward formation of multiple abscesses visible beneath the pleura, as slightly raised, yellow areas. Visi- ble on section in deeper parts. Pneumonic lung may be red. More often grayish in color. Due to filterable virus plus B. pyocyaneus* Heart. Usually normal. Filterable virus le- sions consist of petechiae and ecchymoses which are visible on the surfaces of the auricles, usually the left. Sometimes congestion of coronary ves- sels. Heart itself rarely the seat of secondary le- sions. Epicarditis and pericarditis often result from secondary infection with Bact. suisepticum. Spleen. Sometimes normal or slightly en- larged. Very small bright-red protruding hem- aHog cholera virus is only one of several influences capable of producing primary changes which, in the presence of secondary- invasion with either Bact. necrophorus or B. pyocyaneus may re- sult in the lung lesions mentioned in connection with these organ- isms. For instance, we regard lung worms in combination with B. pyocyaneus as a frequent cause of pneumonia in pigs. 48 PLATE 4. Spleens showing hemorrhages which are rather typical of acute hog cholera. These hemorrhages are observed in only a small per- centage of cases 49 50 HOG CHOLEKA orrhages beneath capsule are normal. These are frequently on ventral surface near the hilus, not so often along the borders and on the dorsal sur- face. Characteristic filterable virus lesions con- sist of black, well defined slightly raised hemor- rhages % to 2 centimeters in diameter, located practically always somewhere on the margin. Spleen may be enlarged, dark, friable, engorged with blood. Due usually to secondary invasion with B. suipestifer, sometimes to other causes. Not of much diagnostic value as related to hog cholera. Liver. Macroscopic appearance usually nor- mal. Very exceptionally ecchymoses, seemingly due to hog cholera virus, are visible beneath the capsule. Often shows degenerative changes, probably due to hog cholera virus, but by no means characteristic, as they may be due to a variety of causes. Kidney. Very rarely normal. Seat of the most characteristic and constant hog cholera le- sions, consisting of petechiae. Organ may be changed as follows: Normal in color, capsule peels easily. Surface of kidney studded with petechiae which appear beneath the capsule, involving the glomeruli as well as other parts. On section, the petechiae are seen variously distributed in the cortex, in the medulla, and sometimes in the membrane of the PLATE 5. Kidney of pig showing numerous petechiae due to acute hog cholera. Often these petechiae are so small and few in num- ber that it is necessary to examine the kid- ney very closely in a good light in order to observe them. The capsule is removed in order to make them more plainly visible n 52 HOG CHOLEBA renal pelvis. They are du-9 to the filterable virus. Engorged with blood. Capsule peels easily. Petechiae distributed as already described. Tend- ency toward more and larger hemorrhages. Changes usually due to filterable virus. Bact. suisepticum or B. cholera suis may be secondary invaders. Very light in color, " cooked kidney. " Capsule peels easily. Marked evidences of degeneration. (Cloudy swelling and granular degeneration.) Petechiae distributed as already described. All changes probably due to filterable virus. Very light in color. Capsule peels easily. No petechiae. Seen most frequently in chronic hog cholera. Changes often due to filterable virus, but not characteristic of it. Very light in color. Capsule peels with diffi- culty, may be thickened. Evidences of degenera- tion followed by increase in interstitial tissue, and chronic nephritis. Primary degeneration prob- ably due to filterable virus. Nephritis due to sec- ondary causes. All of these changes of little diagnostic significance. Considered in general, these petechial hemor- rhages, in the kidney are rarely due to influences other than hog cholera virus. Exceptionally they may be due to Bact. suisepticum, acting either as SYMPTOMS AND LESIONS 53 a primary or secondary influence. There is a tendency by no means constant, and of little diag- nostic significance, for larger and less well defined hemorrhages to appear under the influence of Bact. suisepticum. There is also some evidence, as yet poorly substantiated, that very exception- ally Bact. necrophorus produces petechiae in the kidneys of hogs. This should be regarded as a remote possibility occurring only in association with extensive necrotic lesions in other organs. Bladder. Sometimes normal. Mucosa slightly congested, due to hog cholera virus or other causes. Mucosa dotted with petechiae, due usu- ally to hog cholera virus. Sheath. Often normal. Sometimes distended with foul smelling, discolored urine. Catarrhal inflammation of mucosa. Condition not charac- teristic of hog cholera. Found in other diseases, especially those resembling rheumatism. Lymph glands. Sometimes normal. Typical filterable virus lesion consists of congestion or hemorrhage which appears first in the cortex of the gland, and which may later involve the entire structure giving it a uniform dark color on section. Petechiae are rarely present. Edema frequently pronounced. Permanent enlargement and casea- tion occur in chronic hog cholera. Rare for all glands to show macroscopic changes. Glands 54 HOG CHOLEEA most frequently affected are the gastrics, hepatics, superficial inguinals, lumbars, submaxillaries and mediastinals. PLATE 6. Lymph glands of pig showing hemorrhages caused by acute hog cholera. Left, darkened surfaces of glands. Above, sectioned surface showing hemorrhages around the periphery and in the sinuses. Eight, darkened gland with small section cut away to show peripheral hemorrhages Skin. Often normal. Typical filterable virus lesions consist of purplish discoloration, repre- senting marked congestion or diffuse hemor- SYMPTOMS AND LESIONS 55 rhage. Ecchymoses more rarely visible. Ulcers, apparently originating in these ecchymoses some- times occur on throat and between forelegs. (In hot weather purple discoloration appears a few hours after death in hogs, especially fat ones, dead from any cause.) The pathology and microscopic tissue changes produced by hog cholera virus are not well worked out, but nevertheless the relation between primary filterable virus lesions and secondary changes due to other causes is fairly well understood. Let us consider, for instance, lesions of the digestive mu- cosa. Congestion appears first. It will disap- pear or terminate in hemorrhage. Following hemorrhage, regenerative or degenerative pro- cesses will occur. The degenerative processes may result in destruction and excoriation of the epithelial cells, leaving an unprotected surface in contact with the intestinal contents. Individual resistance and the bacterial flora of the intestine will determine future developments. Regenera- tion will rule, or secondary infection will take place. If Bact. necrophorus is present in suffi- cient numbers, necrotic enteritis will be produced. If B. suipestifer exists in overpowering numbers, the familiar " button ulcer " may develop. In the intestine, we find the primary lesions due to the filterable virus most frequently in the cse- 56 HOG CHOLERA cum and upper colon, and as would be expected, we find the secondary lesions distributed in pre- cisely the same manner. If we examine a hog dead of cholera after a short sickness we encoun- ter intestinal lesions in which congestion, hemor- rhages and early evidences of degeneration pre- dominate. In hogs that have been sick longer, autopsies often reveal a surprising variety of le- sions which collectively encompass effects of the struggle between degenerative and regenerative forces, and which reach their most typical form in the "button ulcer. " In considering thoracic lesions, the same general principles apply. If we inject a pig with filtered hog cholera virus, and kill it about seven days later, the lungs, if affected, will show petechiae and ecchymoses, most likely appearing on the cephalic and cardiac lobes, but not always confined to these parts. There may also be congestion of the mucosa of the air passages. Both changes are due to the filterable virus. What result would we expect if a secondary invader, capable of producing inflammatory changes, should find its way into lesions thus prepared? Obviously we would expect to find bronchopneumonia, occurring most regularly in the cephalic and cardiac lobes but not always thus limited. It is significant that this is the exact picture presented when secondary infection with Bact. suisepticum takes place. SYMPTOMS AND LESIONS 57 The urine of hogs suffering with cholera often contains albumin in excessive amounts, and the chlorids frequently are diminished in quantity, or present only in traces. Contrary to what might be expected, blood and hemoglobin are absent, al- most without exception. CHAPTER VI DIAGNOSIS, DIFFERENTIAL DIAGNOSIS, PKOGNOSIS EARLY and correct diagnosis of hog cholera is essential in coping with the disease effectively. Often an entire herd is in jeopardy, and if hog cholera is present prompt preventive measures must be taken to save it. The diagnosis involves no great difficulties when many hogs are sick, but in the early days of an outbreak when peracute or otherwise atypical cases are likely to occur, puzzling situations arise which sometimes cause costly delay. Thus in exceptional cases we are justified in making a provisional diagnosis of hog cholera, and in handling the herd in exactly the same manner as we would were a positive diagno- sis possible. Experience has taught that we should not be too conservative in regard to taking such a course when the history suggests the dis- ease and when valuable animals are at stake. In seeking to determine the presence of hog cholera we depend on four considerations: 1. History of the outbreak. 2. Symptoms. 3. Lesions. 58 DIAGNOSIS, DIFFEBENTIAL DIAGNOSIS, PROGNOSIS 59 4. Animal Inoculation (rarely applicable). History. Securing the history of an outbreak of suspected hog cholera is simply applying knowl- edge of the ways in which the virus spreads. Usually we find that a hog has died of an unknown cause and. a few days later sickness has appeared among its associates. Careful inquiry should be made regarding recent introduction of hogs into the herd, existence of swine disease in the vicinity, adjacent arteries of traffic and source of feed and water supply. Stockyard hogs and others intro- duced without clear history of previous health should remain under suspicion. Even though they do not themselves contract the disease they may act as intermediate carriers. There is no evidence that hog cholera virus travels through the air but a road or railroad right-of-way may be contaminated by the drip from infected wagons or cars. If the herd is subsisting on garbage and is not immune the circumstances suggest hog chol- era. If kitchen swill is being fed inquiry should be made as to whether the kitchen is supplied with market pork.1 In general the facts brought out by the history of an outbreak simply constitute supplementary 1 In one instance that came under our observation an outbreak of hog cholera was traced to meat trimmings that were placed in a poultry house. Two small pigs formed the habit of escaping from the pen and eating freely of these trimmings. Both devel- oped hog cholera simultaneously, and later transmitted it to their associates. 60 HOG CHOLERA evidence tending either to affirm or deny the pres- ence of hog cholera. Unless there is a definite history of direct exposure the history in itself is not conclusive. Symptoms. Unless several animals are sick it is seldom possible to make a positive diagnosis based on symptoms alone, but the experienced ob- server is usually fairly certain of his ground. It is essential to remember that early in an out- break we do not observe the greatly emaciated hog with arched back, straight tail and drooping ears which has been so frequently described and photographed, and which is the product of long sickness. It should also be kept in mind that many of the symptoms observed in acute hog cholera are present in other diseases, and that all of the symptoms that characterize the disease, do not often appear in one animal. Special consid- eration must be given to a restricted number of the more characteristic symptoms. In examining a herd for suspected hog cholera one should first see it unaffected by artificial ex- citement, taking care to observe a tendency in individuals to chill and crawl beneath the litter. Then the animals may be tempted from the nest with feed, observation being made for any that are reluctant to move, or that stagger or weave in the hind quarters. The animals that come greedily to the trough but leave for the nest in advance of DIAGNOSIS, DIFFERENTIAL DIAGNOSIS, PROGNOSIS 61 their associates, dropping slowly to sternal recum- bency with their snouts half buried in the litter should be regarded as probable cases of hog chol- era, especially when intermittent attacks of chill- ing are observed. Temperature is an important guide, but great care must be taken in securing and interpreting readings. Normal temperatures of hogs vary be- tween 101° and 104° F. and independent of dis- ease, excitement or exertion causes a more rapid temperature elevation in swine than in other ani- mals. Docile adult breeding animals in medium flesh are inclined to show readings near 101° F., while those of young pigs and fat hogs tend to ap- proach 104° F. In taking temperatures of pigs, the thermometer, preferably one with pear or globe-shaped bulb and at least five inches long, should be inserted almost full length. Otherwise many inaccuracies (readings too low) will occur, because a pig, especially if held by the hind legs, will often relax the rectum as long as the ther- mometer remains in position. Chasing pigs to catch them often elevates their temperatures rapidly, and should be avoided. It is important to keep in mind the usual hog cholera temperature curve. In the typical case of the acute form of the disease the curve rises rapidly at the onset of the attack and reaches an elevation between 106° and 107° F. in less than 62 HOG CHOLERA forty-eight hours. This level is maintained for about four days and is followed by a sharp decline which may bring it near normal for a few hours. Then there is an upward trend which carries it near the former high level in which position it may be maintained, or it may fluctuate somewhat violently from day to day. Sometimes it remains elevated until death takes place, but usually it sinks below normal a short time before the pig dies. Thus it is always well to secure temperatures of hogs recently affected, and to be cautious in regard to making a negative diagnosis on the strength of a limited number of temperatures near normal. Several readings near or above 106° F., supported by other suspicious symptoms and a history that indicates hog cholera, may rightly form the basis for a provisional diagnosis. On the other hand, a considerable number of tempera- tures below 104° F. in sick hogs, strongly suggests some other disease. Between these extremes the readings are less conclusive. In this country, and in others where swine ery- sipelas is not prevalent, the characteristic diffuse purplish discoloration which appears on the belly, ears and snout is pathognomonic of hog cholera, but it is observed in relatively few cases. If this discoloration is not observed before death it is of no significance, for it may occur as a post-mor- DIAGNOSIS, DIFFERENTIAL DIAGNOSIS, PROGNOSIS 63 tern change in swine dead from any cause, es- pecially fat hogs that have died in hot weather. Other less characteristic symptoms add evi- dence, but most of them may result from causes other than hog cholera, and it is unsafe to give them too much weight in their relation to diagno- sis. Lesions. Lesions constitute our most accurate guide in diagnosing hog cholera, for it is not often that a conclusion can be reached without consider- ing them. Hogs sometimes die of the disease without showing any characteristic macroscopic tissue changes, so if no cause for death is found, additional autopsies should be performed. In case it is necessary to kill a pig for this purpose, it is best to select one that has been sick several days, but not a chronic case. Petechiae and ec- chymoses are the chief changes which character- ize hog cholera, but it is important to remember that in cases of long standing, and in those in which secondary invasion has taken place these primary filterable virus lesions may be so changed in character that they are difficult to identify. Assuming that we have before us a carcass, and that hog cholera is suspected, the autopsy will in- clude special examination of the skin, kidneys, bladder, lymph glands, spleen, heart, lungs and laryngeal mucosa, as well as the serous membranes readily accessible, and the digestive tract. The 64 HOG CHOLEKA changes which appear in these various parts have already been discussed, so for our present purpose we will consider chiefly those which are of primary importance in their relation to diagnosis. The skin is examined for ecchymoses and yel- lowish-brown ulcers which sometimes appear on the throat and other ventral surfaces. If there is a purplish discoloration, inquiry should be made as to whether it was noticed before death took place. An affirmative reply suggests hog cholera, while a negative one practically dismisses the le- sion from consideration. Changes in the skin are frequently absent. As we open the thoracic and abdominal cavi- ties petechiae and ecchymoses are sometimes ob- served in or immediately beneath the serous sur- faces thus exposed. They appear infrequently in the parietal pleura and parietal peritoneum and are somewhat more common in the serous coat of the intestine, especially that of the cecum and colon. The kidney lesions are highly characteristic of hog cholera, and they occur in nearly all cases. They consist of petechiae which are distributed on the surface, as well as in the deeper structures. These are dark red in color and sharply defined, often giving the organ the "turkey egg" appear- ance. Sometimes they are so few in number that the capsule must be removed in order to see them, DIAGNOSIS, DIFFEBENTIAL DIAGNOSIS, PEOGNOSIS 65 care being taken to make the examination in a strong light. Infrequently other causes produce peteehias in the kidneys of swine, but in this coun- try, unless another cause is apparent, either by virtue of the history or accessory lesions, we are safe in attributing them to hog cholera. Petechiae in the mucosa of the bladder occur in most cases of hog cholera, and they do not often result from other causes. The serous surface is practically always normal. Some of the lymph glands are usually involved, and to the experienced observer the changes in them aid greatly in making a diagnosis. On the surface the gland is very dark red, almost black. On section the periphery is similar in color, while the deeper structures may remain unchanged. It is important to bear in mind that any inflamma- tory process may affect adjacent lymph nodes, and to make allowance for this fact, but marked per- ipheral congestion or hemorrhage, when observed in several glands widely separated, in the absence of apparent inflammation in adjacent structures, strongly indicates hog cholera. The spleen reveals characteristic hog cholera le- sions only in the dark, swollen circumscribed hem- orrhages, usually less than 1 centimeter in diam- eter, which appear along the border. In field cases that have died of hog cholera these lesions are not often observed, because secondary invad- 66 HOG CHOLERA ers have so enlarged and darkened the entire or- gan as to render them invisible, and because post- mortem changes take place rapidly. The enlarged, dark, pulpy spleen which is often encountered in hog cholera outbreaks is of little significance in diagnosis, because it is so frequently the result of other causes. The heart reveals no macroscopic lesions in the vast majority of cases, but the petechiae which are sometimes visible on the left auricle, less fre- quently on the right, and rarely involve the ven- tricles, are usually caused by hog cholera virus. The lungs are often normal. If the surfaces are dotted with ecchymoses, the fact suggests hog cholera quite strongly, but occasionally these le- sions are due to other causes. The laryngeal mucosa is often the seat of pete- chiae, which are characteristic of hog cholera. Examination of the intestinal mucosa often aids in making a diagnosis, but the lesions encountered are often difficult to interpret. Certain irritants cause changes which may be confused with those due to hog cholera, and secondary invasion tends rapidly to modify filterable virus lesions so that they are difficult to identify. Ecchymoses and larger hemorrhages, as well as ulcers of recent origin, when distributed near the ileocecal valve and elsewhere in the mucosa of the caecum and upper colon, may be accepted as supplementary DIAGNOSIS, DIFFEBENTIAL DIAGNOSIS, PKOGNOSIS 67 evidence of acute hog cholera. The "button ulcer" is usually associated with the chronic form, but agents other than the filterable virus may be instrumental in producing it. All these hog cholera lesions will not often be found in one animal, but if two or more organs are involved this fact, supported by a history that does not positively deny the presence of the disease, may be accepted as ground for a diagnosis. If more organs are involved the evi- dence is more conclusive. AnimaJ inoculation. This method is rarely applicable in actual practice, because it is expen- sive and requires too much time. In very excep- tional outbreaks which present atypical features, and in cases, involving litigation it may be useful. The essentials -of a conclusive experiment may be sunrniarized" thus :. 1. Blood should be drawn from a hog which has been sick for only a short time, and which carries a temperature near 106° F. 2. The . blood -should be diluted with sterile water and passed through a filter which retains all microscopic organisms. 3. Enough of the filtrate to represent at least 1 mil of the undiluted blood should be injected into a susceptible pig, preferably one weighing between forty and one hundred pounds. 4. Twelve days previous and subsequent to the 68 HOG CHOLERA date of injection the pig should be protected from extraneous hog cholera infection; all receptacles and instruments used in making the injections should be sterilized. 5. Symptoms of hog cholera should appear in less than eight days following the injection. 6. The pig should die in less than seven days following the appearance of symptoms, or at the end of that time, providing it is still sick, it should be killed. 7. Autopsy should reveal typical hog cholera lesions in at least two organs. 8. In negative experiments the susceptibility of the experimental pig should be proved by a subse- quent injection with at least 1 mil of virulent hog cholera blood. Differential Diagnosis Peculiar difficulties are met in the differential diagnosis. Clinical examination of the individ- ual is subject to limitations which are not encoun- tered in dealing with larger animals, and some of the maladies which we seek to differentiate from hog cholera occur so frequently in combination with that disease that we do not always have well defined features upon which to base our conclu- sions. Thus under certain circumstances we have not only to decide whether a given outbreak is hog cholera or swine plague, but we must also DIAGNOSIS, DIFFEKENTIAL DIAGNOSIS, PROGNOSIS 69 ask ourselves whether the two diseases exist in combination. Laboratory examinations may dem- onstrate the presence of a bipolar organism, but they cannot in the course of a few hours deny the presence of the hog cholera virus, and thus they are often dangerously misleading. Return mail diagnoses of " swine plague" or "hemorrhagic septicemia" are without value because they ignore consideration of hog cholera virus, which in this country is present in most outbreaks of rapidly transmissible swine disease. Among the diseases from which hog cholera must be differentiated are uncomplicated swine plague, pneumonias due to a variety of causes, sep- ticemias, tuberculosis, anthrax, so-called "flu," various parasitisms, soap poisoning, brine poison- ing, and sudden deaths from such causes as heat- stroke and lightning-stroke. Eouget and rinder- pest are also to be considered in countries in which they are prevalent. The differential diagnosis cannot be made by rule of thumb, nor is it possible to summarize or tabulate the determining features of these va- rious maladies, so that the inexperienced observer can distinguish among them. Armed with defi- nite knowledge of the diseases with which he is dealing the diagnostician usually reaches his con- clusions rapidly and accurately. In the absence of such knowledge, a few rules do not suffice. 70 HOG CHOLERA Having already dealt with the distinguishing fea- tures of hog cholera we will confine our remarks chiefly to characteristics which suggest the pres- ence of these other diseases. Swine plague. Swine plague rarely occurs in pure form, it affects only a portion of the animals in a herd, and there are frequent spontaneous re- coveries. There is often a history of recent ship- ping. The incubation period is short (1 to 3 days), acute dyspnea and thumping are prominent symp- toms, and the hogs show more distress than is observed in hog cholera attacks. High tempera- tures are not the rule except during the first few hours of sickness. The characteristic " swine plague pneumonia, " if present in several autop- sies, speaks for the existence of swine plague, but the absence of the filterable hog cholera virus must be clearly established before a diagnosis of pure swine plague is justified. None of the pneumonias, with the exception of that associated with swine plague, are accom- panied by the lesions in other organs which char- acterize hog cholera. Usually they occur where pigs are kept in very dusty quarters, or where the floors are cold and damp and no dry litter is provided. Eecent shipping is a predisposing fac- tor, and lung worm and ascarid infestations play an important part in their development. They are sporadic or only slowly transmissible. High DIAGNOSIS, DIFFERENTIAL DIAGNOSIS, PROGNOSIS 71 temperatures are not common, and the prominent symptoms grow out of the pneumonia itself. Exceptionally septicemia due to nonspecific or- ganisms may occur, but its features are not well defined. In differentiating we must therefore de- pend on the more definite manifestations of hog cholera. Tuberculosis may only rarely be confused with chronic hog cholera. Hogs following tuberculous cattle and those fed infected creamery by-prod- ucts are most commonly affected. The history of the case should be considered and if doubt remains the intradermal tuberculin test may be applied. If material for autopsies is available, the differ- entiation presents no great difficulties. Anthrax and the peracute form of hog cholera are not always easy to differentiate. If the for- mer disease has existed previously in the locality ; if other classes of live stock are affected; if the hogs show swelling of the throat or froth mixed with blood coming from the mouth or nostrils ; if the blood is black and incoagulable, anthrax should be suspected, and a microscopical examination made. A malady known as * 'state fair disease* ' or "flu" has in recent years been recognized in the central states. It is often associated with a his- tory of recent shipping, respiratory symptoms and lesions predominate, and recovery is the rule. 72 HOG CHOLERA This latter fact alone will distinguish it from hog cholera, when it occurs in pure form. Ascaris infestation and hog cholera sometimes exist in the same herd. As a result of the diar- rhea incident to the latter disease ascarids are frequently evacuated in the feces, and the entire train of symptoms, as well as the deaths, is attrib- uted to the parasites alone. Even though the parasites are present in large numbers, if deaths are numerous, further examination should be made for evidence of hog cholera. Lung worms cause cough, emaciation and other symptoms which resemble those observed in chronic hog cholera. The history of the outbreak, supplemented if necessary by an autopsy, will be sufficient to determine its cause. Chronic hog cholera is usually a sequel of the acute form. Lung worms are often associated with pneumonia, causing death most frequently in young pigs. Unless great care is used these parasites may be overlooked. The smaller air passages should be laid open with sharp shears and the examination made in a strong light. Considered collectively, the various drug and food poisonings differ from hog cholera in that several animals often are affected at the same time, the symptoms as a rule are more violent, vomiting is more common, and temperatures are not so high. The history may reveal the source DIAGNOSIS, DIFFERENTIAL DIAGNOSIS, PROGNOSIS 73 of the particular poison, and some of the drug poisonings (strychnin, belladonna, lead) are in themselves characteristic. Poisoning with the al- kaloids produces no lesions, and no poison, so far as we know, is responsible for changes which are observed in hog cholera. Common salt (sodium chlorid) is especially poisonous for hogs that are not accustomed to it, causing intense inflammatory changes in the digestive mucosa, and congestion of the meninges. Long continued feeding with material containing soap and lye will produce disease resembling chronic hog cholera. How- ever, our task is usually to differentiate between poisonings and acute hog cholera, and this pre- sents no great difficulties if we resort to autopsies, for none of the poisons produce lesions which re- semble those observed in acute hog cholera. In suspected heat-stroke and lightning-stroke, the history is an important guide. Heat-stroke occurs most frequently in fat hogs deprived of shade or water in hot weather, and in those shipped in overcrowded stock cars, or subjected to excitement or violent exertion during the sum- mer months. The hair of hogs dead of lightning- stroke may be seared, there may be arborescent congestion or hemorrhage in and beneath the skin at the point where the current entered the body, and sometimes there are lacerations of the inter- nal organs. Eigor mortis is not pronounced. 74 HOG CHOLERA Rouget or swine erysipelas does not exist in the United States. The septicemic form of the disease resembles hog cholera very closely. It has a shorter incubation period than the latter disease, but resort must often made to microscop- ical examination, in order to distinguish between them. Rinderpest does not occur in the United States, and in countries in which it is prevalent, swine do not contract it readily. For this reason it is not well characterized, but in case of necessity it may be distinguished from hog cholera by nitration experiments in which cattle are used as test ani- mals. Both viruses are filterable, but that of rinderpest is the only of the two which affects bovines. Prognosis In the individual, hog cholera runs a rapid and fatal course, and even when recoveries occur, they may be slow and incomplete. Therefore in all hogs visibly sick the prognosis is bad, but it is the herd as a unit which we must consider, for we are frequently called on to estimate the salvage which may be expected. The ability to do this with a reasonable degree of accuracy is acquired only by experience, and it is a great asset to one who han- dles hog cholera in the field. We can indicate -only the guiding principles upon which the progno- sis depends. 75 The number of animals dead and visibly sick at the time of serum treatment forms our chief basis of estimate. Assuming that a herd is kept under average farm conditions, and that there is no evidence of complications, as a very general rule we expect to save about as many hogs as are eating greedily and are free from abnormal tem- peratures on the date of serum administration. Some of those that show no fever will die, and a few of those that show fever will recover, one class approximately compensating the other. In herds in which it is not possible to secure reliable temperature readings, the prognosis must be more guarded. In general, during the early days of an outbreak, we expect about as many deaths to follow serum treatment as the combined sum of the hogs that have previously died and those visibly sick when serum is administered. If fifty per cent of the animals in a herd are dead or visibly sick we expect the salvage to offset the cost of serum treatment, and leave something to spare, but we cannot promise much in such a herd. Evidence of secondary infection, coexisting par- asitisms, improper feeding and housing, a history of recent shipping or other weakening influences all call for a guarded prognosis. If the hogs have not been confined closely, or if they are in several pens some of which remain uninfected, the prog- nosis is relatively more favorable. CHAPTER VII PREPARATION OF ANTI-HOG-CHOLERA SERUM AND HOG CHOLERA VIRUS WE are indebted to Dr. Marion Dorset and Dr. W. B. Niles of the United States Bureau of Ani- mal Industry for developing our present method of preparing anti-hog-cholera serum. The dis- covery that hog cholera is caused by a filterable virus dismissed further efforts to immunize against it with products of various bacteria, but it suggested hope for a protective serum analo- gous to that used against rinderpest, a filterable virus disease of cattle. That hope was realized in 1908 when Dorset announced his discovery, and although the immediate control of hog cholera which some predicted did not materialize, the ob- stacles encountered have not been due to any fun- damental defect in the serum itself. When prop- erly prepared and used it is one of the most effec- tive biologies known to preventive medicine. Anti-hog-cholera serum production is highly or- ganized and carefully controlled in the United States and many laboratories are in operation which are models for convenience, cleanliness and 76 0 o 2 be- .3 77 78 HOG CHOLEKA sanitation. All laboratories which make inter- state shipments must secure licenses from the fed- eral government and submit to regulations which have been formulated to protect those who use the products. The laboratories must meet certain well-defined requirements before they are allowed to operate, and thus despite great deviation in de- tail, the same fundamental processes are used in all of them. We will consider first the essential requirements for preparing the protective defib- rinated blood, which has been called anti-hog-chol- era serum, and which forms the basis of all the more or less refined products used to prevent hog cholera in the field. Buildings. The buildings should be suited to the conditions under which the laboratory is to operate. These conditions vary so widely that uniformity is neither to be expected nor desired, but certain governing principles should be ob- served in all construction. In general, simplicity, convenience in operation, and provisions for clean- liness are the primary considerations. Future up- keep costs should also be reduced to a minimum in the original construction. Under most condi- tions concrete is the best material to use. The walls, ceiling and floors should be fin- ished so that water will not injure them. The floors should be drained in a sanitary manner. Steam or hot water heat should be provided, the g'S ss =3 O s° Jti 79 80 HOG CHOLERA building should be plumbed for hot and cold water, and all outside doors should be screened in summer. Ample light and ventilation are re- quired. The minimum requirements for reasonable con- venience and cleanliness in a serum laboratory consist of preparation room, bleeding room, serum laboratory proper, office, dressing room and lava- tories, store room and refrigerator room, as well as furnace room and coal bins so situated that dust from them will not contaminate other parts of the building. Quarters for the hogs should be suited to local requirements. In any event they should be at least seventy-five feet from the laboratory build- ing, and even a greater distance is desirable. The floors should be of concrete, well drained, and ample light and ventilation should be pro- vided. Boom for exercise on the ground is desir- able, and pasture for hogs that are to be kept for several weeks is a great asset. Provision should be made for sanitary disposal of manure, and other waste from the laboratory and hog quarters. In general, convenience for those who care for the animals, and cleanliness and comfort for the animals themselves are the chief consid- erations. The equipment of the laboratory is likewise governed by individual needs. Too much equip- PBEPAEATION OF ANTI-HOG-CHOLEKA SERUM 81 ment is a detriment, as methods are constantly changing and improving and each unnecessary fix- ture takes up room and must be kept clean. Es- sential major equipment includes facilities for washing, sterilizing and storing all instruments and containers used, vacuum and pressure tanks connected with motor driven pumps, portable crates for tail bleeding and hypering, portable or stationary tables or stocks for bleeding serum hogs and virus pigs from the throat, scales,v motor driven shaker, serum mixer and office equipment including forms for keeping records. Minor equipment includes bleeding and hyper- ing units, tail shears, clamps, hypodermic syringes and needles, wax heater, cannulas and sticking knives, scalpels, instrument trays, antiseptic con- tainers, funnels, graduates, pipettes, defibrinating forks, porcelain containers for serum and virus blood, apparatus for separating out fibrin and clot, and bottles for storing and shipping. Grouped around this essential unit may be a multitude of accessories, or the unit itself may be multiplied so as to provide for production on a large scale. Facilities for butchering, for cooling carcasses, for rendering virus pig carcasses, for handling virus in separate rooms, for keeping susceptible pigs isolated, for dipping and isolating new arrivals, for bacteriological work, for packing and mailing products, and for exposing serum and 82 HOG CHOLEEA virus pigs to calves so as to guard against foot- and-mouth disease, are just a few of the acces- sories that circumstance must include or elimin- ate. Further detail in regard to equipment cannot be profitably discussed here. In all these things sim- plicity, cleanliness, convenience and low upkeep cost are the chief considerations. Good equip- ment invites clean operations, but in the last anal- ysis the quality of the finished product is not de- termined by equipment. A careless operator will contaminate serum in spite of every convenience ; a careful one will produce clean products under adverse working conditions. 'Principle governing serum production. When a hog contracts cholera and recovers, or when it receives simultaneously hog cholera virus and protective serum, it is thereafter immune to the disease. The body cells, in self-defense, have elab- orated substances, termed antibodies, which neu- tralize the effects of all hog cholera virus subse- quently introduced into the system. In the ordi- nary immune hog these antibodies protect against any quantity of cholera virus to which the animal may be exposed, but they do not exist in sufficient concentration so that the blood may be used to protect other animals. Antibody elaboration must be further stimulated, and this is done by giving the immune an enormous intravenous dose PREPARATION OF ANTI-HOG-CHOLERA SERUM 83 of virulent hog cholera blood. A slight reaction follows, and in the course of a few days the im- mune becomes a hyperimmune and comparatively small doses of its blood will protect other hogs ex- posed to cholera. We are now ready to consider in some detail the various steps required in preparing anti-hog-chol- era serum. In all these it is a principle that the operating room shall be clean and free from dust, that the floor shall be dampened, that the operator shall wear clean clothing and that his hands shall be scrupulously clean. The hands must not touch the serum or virus blood, and all instruments and containers with which the blood comes in contact must be sterilized before use. Antiseptic solution should be applied by means of a gravity irrigator or some other device which prevents the hands from passing alternately between operating field and antiseptic container. Exact records of each operation must be kept, and each hog used must be identified with a number tag. Immunizing. Requirements. Two hypodermic syringes, one ten mil capacity or less, for virus, the other twenty mil capacity or more, for serum ; scrub-brush and antiseptic solution, also anti-hog- cholera serum and hog cholera virus each in a separate, covered receptacle. The pig is held by an assistant and the skin covering both armpits (or the inner region of both 84 HOG CHOLEKA hams) is thoroughly scrubbed with antiseptic so- lution. Then two mils of virus are injected into one armpit, and the required quantity of serum (about 35 mils for a 100 pound pig) is injected into the other. Deep injections are desirable. Following this treatment the pig undergoes a reaction beginning in about five days and lasting about a week, during which time a permanent im- munity to hog cholera is established. It is de- sirable to immunize prospective hypers as com- paratively young shoats and to delay hypering until they have attained a weight of at least two hundred pounds, as a long interval between the date of immunizing and that of hypering favors potent serum. In no instance should this interval be less than sixty days. The Virus Pig In order that the immune may receive addi- tional virus and become a hyper, a supply of virus must be procured. This is done by injecting sus- ceptible shoats with lethal doses of hog cholera virus and collecting their blood after they sicken with the disease. A virus pig should be in thrifty condition, weighing near one hundred pounds. It should not be heavily infested with parasites. The dose of virus (about 2 mils) is injected in the same manner as has already been described, but no protective serum is given. PEEPAEATION OF ANTI-HOG-CHOLERA SEBUM 85 Four or five days subsequent to injection the pig should show a temperature near 106° F., and a day or two later marked symptoms of hog chol- era should appear. As a very general guide it may be said that a virus pig is ready to bleed when it has carried a high temperature for about three days and when it has shown severe symptoms of hog cholera for about two days. A good strain of virus will bring this about in approximately seven days subsequent to the date of injection. The time required may be extended in certain individ- uals, but a virus that regularly requires more than eight days in which to ' ' ripen ' J pigs for bleeding is not desirable for hypering. Bleeding the virus pig. When the sick pig is ready to bleed for virus it is taken to the labora- tory. In the preparation room the entire body is washed, and the animal is secured to a tilting operating table, revolving door or other device for securing it by the hind legs and suspending it head downward. The front legs are secured well apart and the snout tied backward, stretching the skin covering the throat. The throat and sternal region are then thoroughly lathered (an antiseptic soap is desirable), carefully shaved and rinsed, and an antiseptic solution is applied. If it is a male pig a clamp is attached to the prepuce to prevent dribbling of urine. Finally the entire body is covered with a cloth, previously dampened 86 HOG CHOLERA in antiseptic solution, leaving only the throat ex- posed, and all is ready to draw the blood. An ordinary two-quart fruit jar, previously sterilized, is a good receptacle. The sticking may be done with a large cannula designed especially for the purpose, or with a narrow bladed knife. In case a knife is used the hand should be held low on the throat so that the blade passes directly upward, the back against the dorsal surface of the sternum. The blade should not leave the median line, but should be forced upward until it severs a carotid or the anterior aorta near the bifurcation. A free clean incision made in withdrawing the knife facilitates rapid and complete bleeding. A pig weighing one hundred pounds should yield about one thousand mils of blood. If pigs are killed too late, after they are very weak, the yield is greatly reduced. Handling the virus blood. Immediately after the blood is drawn it is defibrinated. This is done by closing the receptacle tightly and shaking it vigorously for a few moments. It is then marked for identification and placed in ice- water pending the time when the pig that yielded the blood can be autopsied. Assuming that the autopsy, which will be considered later, has been satisfactory, the next step is to separate out the fluid part of the blood, leaving the clot and fibrin behind. This is accomplished in various ways. Some use a cen- PEEPABATION OF ANTI-HOG-CHOLERA SERUM 87 trifuge of which the essential part is an enclosed, revolving, perforated cylinder; others pour the contents of the jars directly into funnels into which one or more thicknesses of sterile gauze have been placed ; still others empty the jars into perforated funnels which fit into the tops of tall re- ceptacles into which the fluid drains, and near the bottom of which is a turncock for drawing it off. Formerly clot presses were used universally as a final means of extracting the last drop of blood from the fibrin and clot, but this practice is gradu- ally being abandoned. It increases the yield but little, and adds unnecessary debris to the blood, whether it is serum or virus. In all methods of handling the final act is to strain the blood through gauze, after which it is placed in storage bottles and refrigerated pending the time when it is re- quired for hypering. The blood of several virus pigs is mixed after autopsies have confirmed its fitness for use. This "hypering virus " may be kept forty-eight hours or even longer, but it is best to use it after it has been refrigerated about one day. It is well to strain it a second time just before it is to be in- jected. Preservative is never added to hypering virus. The autopsy. The two essential requirements for a virus pig are that it shall show complete evi- dence that it was suffering with acute hog cholera 88 HOG CHOLERA at the time it was killed, and that it shall be free of other infectious diseases which may be trans- mitted through its blood. The clinical history of the pig, and more especially the autopsy, enables us to select on this basis. If in addition to a clini- PLATE 9. Post-mortem room where autopsies on virus pigs are held. Each pig must show marked lesions of acute hog cholera, and must be free from other infectious diseases. (Courtesy Pitman-Moore Biological Laboratories.) cal history suggesting hog cholera a pig shows characteristic lesions of the disease, slight or se- vere, in two or more organs, we consider the first requirement satisfied. Generalized tuberculosis disqualifies, but slight and localized tubercular le- PREPARATION OF ANTI-HOG-CHOLERA SERUM 89 sions do not cause rejection. Here, we believe, a very rigid interpretation is advisable, and in all cases which admit doubt the pigs should be re- jected. Pigs that show enormously enlarged, dark, pulpy spleens as well as those that bleed scantily and yield very dark blood do not produce satisfac- tory virus. The tendency in both cases is for the blood to defibrinate imperfectly and when it is mixed with good virus the entire lot may be ruined. In the routine autopsy the skin, and all of the thoracic and abdominal viscera are examined, as well as the submaxillary and superficial inguinal lymph glands. In case of doubt, due to slight le- sions, the mucosa of the larynx and popliteal lymph nodes should be included. Disposal of carcass. Virus pig carcasses may be burned or rendered as circumstances direct. The Hyperimmune The immunes which are to be hyperimmunized and later yield serum should be carefully selected. The longer they have been immune to hog cholera, the better. They should be hearty feeders, in moderate flesh, and always strong and active. The ears should be moderately large, but thin and well veined, and the tail at least of average length so as to permit the required number of bleedings. 90 HOG CHOLEKA A weight near two hundred pounds is desirable. The intradermal tuberculin test should be applied to prospective hypers, and all reactors rejected. Hypering. The immune is confined in a port- able crate and the snout is secured firmly, drawing the head to one side. Its weight is then obtained and recorded, and it is wheeled to the preparation room in the laboratory. The entire body is wet thoroughly and a cloth dampened in antiseptic so- lution is thrown over it, leaving only the head ex- posed. One of the ears is lathered, shaved, rinsed and washed in antiseptic solution and the hog, thus prepared, is wheeled to the hypering room to receive the required dose of virus. The hypering operation consists of injecting into an ear vein five mils of virus blood for each pound the hog weighs. The virus is placed in a graduated bottle which is closed with a rubber stopper, perforated in two places. Through one opening is passed a curved nickeled tube which, ex- tending to the bottom of the bottle, serves as an outlet for the virus when air pressure is applied ; through the other is passed a shorter tube extend- ing just through the stopper and through which air is pumped to produce pressure. Both are ex- tended with rubber tubing, the intake being thus connected with a tank containing compressed air, and the outlet terminating in a slip fitting for the hypodermic needle which is to be introduced into PEEPAEATION OF ANTI-HOG-CHOLEKA SERUM 91 the ear vein. On this outlet tube is a pinch-cock to control the flow of virus. The bottle is filled with virus, the stopper is forced down tightly with PLATE 10. A close view showing the hypering process. A 200 pound cholera immune hog receives 1000 mils of virus in the ear vein. In ten days the animal is ready to bleed for protective serum. New York State Veterinary College at Cornell University 92 HOG CHOLERA a screw clamp, enough virus is passed through the system to eliminate danger from air bubbles, the pinch-cock is closed, and all is ready to make the injection. The vein into which the needle must be intro- duced usually conforms roughly to the contour of the outer margin of the ear, and is about one inch removed from it. A spring clamp is ap- plied near the base of the ear, thus compressing this vein and rendering it plainly visible. The ear is drawn taut with the left hand, and with the right the needle is thrust quickly into the vein, passed rapidly along its course about two inches, and secured in position with the clamp which is no longer needed to compress the vein at the base of the ear. If the needle is properly in place there will be a backward flow of blood through it. With- out a moment's delay it is now necessary to con- nect the needle with the supply of virus under pressure, and to open the pinch-clock allowing the virus to flow into the circulation. Otherwise the hog's blood may clot in the needle rendering the injection impossible. When the flow of virus is established, one must see that the needle is re- tained in place until the required quantity, al- ready determined, has been injected. This will require from four to thirty minutes, the time be- ing governed by the degree of pressure applied, by the size of the needle and the accuracy with PREPARATION OF ANTI-HOG-CHOLERA SERUM 93 which it has been placed in the vein, as well as by individual differences in hogs that are not well understood. When the required quantity of virus has been injected, the pinch-cock is closed, the needle is withdrawn, and the hog is wheeled away and released. This describes the hypering operation in its simplest form with everything favoring the oper- ator. Volumes could be written about the at- tempts that end in failure. Practice is important, but a natural surgical touch amounting almost to instinct is required of the expert operator, and even he may experience unexplainable lapses in the execution of his technique. However, most of the annoyances experienced may be overcome, and it seems desirable to include a few suggestions which may aid the beginner in his work. At first select hypers with ear veins straight and prominent; later it will be possible to hyper practically all subjects : begin the operation soon after the ear has been shaved ; otherwise the vein may recede and be very difficult to distend so that the needle may enter it : use a needle with a per- fect point ; a dull one will roll the vein under it : Hold the ear out straight; otherwise the skin will be relaxed and the vein will be unnecessarily tor- tuous : after the needle has entered the vein do not release it until it is clamped firmly in position; the nub may drop carrying the point upward and 94 HOG CHOLEEA causing it to prick through the wall so that virus will escape from the vein and accumulate in the surrounding tissues when it is applied under pres- sure : if the needle tends to pucker the skin at the point of entrance, dampen both needle and skin (an atomizer containing alcohol is convenient for this purpose). In inserting the needle hold the index finger of the right hand well toward the point, between the ear and the needle; it is im- possible to guide a needle when it is grasped at the nub only: if when pressure is applied virus is seen to escape from the vein and accumulate in the surrounding tissues, release the pressure at once ; otherwise all chance of entering the vein in subsequent trials will be destroyed. Before inserting the needle some operators connect it directly to the rubber tubing containing the virus under pressure, thus obviating annoy- ance incident to blood clotting in the needle or to accidental breaks in the slip connection due to struggling on the part of the hog. When this technique is employed one must depend largely on his sense of touch to determine when the needle is in position, for backward flow of blood cannot be observed. In case of doubt as to whether the needle has entered the vein, one may compress the tubing between the pinch-cock and the needle, at the same time observing whether the virus thus PREPARATION OF ANTI-HOG-CHOLERA SERUM 95 forced out follows the course of the vein or is dis- tributed in adjacent tissues. Occasionally one encounters a fleshy-eared hog exhibiting no ear vein which is visible to the naked eye in ordinary light. Subjects of this kind may usually be hypered by darkening the room and holding an electric light bulb directly under the ear. Small, deeply covered veins are thus ren- dered plainly visible, and hypering is accom- plished with surprising ease. Bangers and accidents due to hypering. The ordinary immune hog will tolerate, without inci- dent, intravenous injection of five mils of virus per pound body weight. Usually there is no evi- dence of pain or distress, and the animal lies quietly while the dose is being administered. In exceptional cases, however, sudden death occurs. It is a curious fact that if distress is to appear, it becomes evident before the first half of the dose enters the circulation. Thus it is not quantity alone that kills. Other factors may contribute, but the principal one seems to be failure of nerv- ous control over capillary contraction. The capillary walls fail to adjust themselves to the increased pressure, and as a consequence distend and rupture. Usually the lungs alone bear evi- dence of this fact, as they contain the first set of capillaries through which the foreign blood must 96 HOG CHOLEKA pass, but occasionally the effect is observed in the skin. Severe and general congestion, interspersed with areas revealing slight or extensive hemor- rhage, are the usual changes observed in the lungs. Prevention of sudden death resulting from hy- pering is not always possible. Fatalities occur much less frequently if the virus used is first thoroughly cooled. Even ordinary refrigerator temperatures are not objectionable. As a second precaution a close watch should be kept on the hog during the process of hypering, though it is not always possible to distinguish between struggles due to fright and perversity and those due to genuine distress. Real danger is marked by a sudden inspiratory gasp or rapidly developing dyspnea, especially when these symptoms are ac- companied by violent struggling and nervous symptoms such as twitching of the snout or eye- lids and protrusion or shuttling of the eyeballs. If distress is not severe the flow of virus may be checked momentarily and then allowed to con- tinue slowly, but as a rule it is best to release the hog and take no further chances. Usually in sub- sequent trials these hogs will tolerate hypering without incident. Sometimes it is not until the hog is released from the crate that we observe symptoms. Vomit- ing occurs somewhat frequently at this time but PREPARATION OF ANTI-HOG-CHOLERA SERUM 97 it is of no particular consequence. Great prostra- tion and severe dyspnea are the symptoms which suggest impending death, especially when foam colored with blood exudes from the mouth or nos- trils. Hogs suffering thus should be kept cool, their heads should be elevated, and they should not be subjected to unnecessary handling. Some will recover spontaneously. In fatal cases coma and shallow breathing precede death. We have tried hypodermic doses of strychnin under such conditions, but while temporary relief is afforded the treatment seems merely to delay death rather than to prevent it. Fatalities sometimes occur when air is pumped into the vein. These may be avoided by forcing the outlet tube completely to the bottom of the bottle, and by allowing, previous to each opera- tion, a quantity of virus to pass through the out- let sufficient to carry away bubbles that may be accumulated in the rubber tube. Air in the vein does not always cause death, but the risk is great, and avoidable. Deaths from hog cholera as a result of hypering are practically unknown, except in hogs that have been purchased without a clear history of having been properly immunized. During the interval between the date of hyper- ing and that of the first bleeding for serum, about ten days, careful observations of the hyper are 98 HOG CHOLEEA necessary. The points to be determined are whether the hog has been vigorous and healthy, and whether this condition still prevails at bleed- ing time. Temperature readings, clinical obser- vations and comparative weights are the sources of information, each being employed as circum- stances direct. The average hyper shows a mod- erate and transitory fluctuation of temperature immediately following the dose of virus, and he may eat indifferently for a day or two, but as a rule his appetite is unimpaired, and he continues to gain in weight about a pound per day. If a hog's appetite has been greedy during the last seven days preceding the date of bleeding ; if there has been no loss in weight or outward evidence of sickness ; and if the temperature is normal when bleeding time arrives, we consider the animal a fit subject to produce serum. Bleeding for serum. The hog is confined in a portable crate and wheeled to the preparation room. Bleeding is to take place from the tail which now requires thorough mechanical cleans- ing. Warm water and antiseptic soap are applied freely and a stiff scrub-brush is used to work up a lather. After several minutes of scrubbing, the tail, and a circular area surrounding its attach- ment, are carefully shaved. The body of the ani- mal is then wet to settle dust that may be con- tained in its coat, and a cloth dampened in anti- PLATE 11. Bleeding unit, and hog prepared for bleeding, but still uncovered. The fruit jar and breeding horn are clamped together and sterilized as a unit. The rubber cap is removed from the mouth of the horn immediately before the latter is applied to the hog's tail. New York State Veterinary College at Cornell University 99 100 HOG CHOLEKA septic solution and containing a hole through which the tail protrudes, is thrown over the body. Thus prepared, the animal is ready for the bleed- ing room. Bleeding is accomplished with vacuum which hastens the process and retards coagulation. The essential bleeding unit consists of a curved metal horn, one end armed with a fitting which receives the mouth of a two-quart fruit jar, forming an air tight joint, and the other consisting of a round or oval-shaped opening presenting a moderately broad surface to be pressed firmly against the skin surrounding the tail, which member the horn en- closes. Communicating with the interior of the unit is a tube which, continued with rubber tubing, connects with a pipe leading to a vacuum tank. Somewhere in the line is a turncock so situated that vacuum may be employed or released at will, and between this and the bleeding unit is an intake valve fitted with a small cup containing carbolized cotton through which air must pass to release the vacuum remaining in the unit when bleeding is completed and the turncock is closed, severing connection with the vacuum tank. A vacuum indi- cator is inserted in the line between the tank and the turncock. The operator grasps the tail, disinfects it thor- oughly, and dries it with alcohol. Then with shears designed especially for the purpose an inch PLATE 12. Bleeding for p^rum. Vacuum is applied through the rubber tube, and the blood flows into the jar. 1000 mils of blood can be drawn in about 8 minutes. New York State Veterinary College at Cornell University 101 102 HOG CHOLERA or more is clipped off the end, and the part re- maining is guided into the bleeding horn, which is forced tightly against the body. When vacuum is applied the contact is rendered air-tight, and blood streams rapidly from the severed tail. Moderate and uniform traction should be applied during the process of bleeding. When the desired quantity of blood has been drawn, the turncock is closed, the vacuum remaining in the unit is re- leased through the intake valve already described, and the tail is ligated near the end or the raw sur- face is seared to prevent further hemorrhage. It is well to cover all the shaved surfaces with ointment thus preventing chapping of the skin which may render subsequent bleedings difficult. Bleeding technique is a determining factor as far as cleanliness of the serum is concerned, and too much importance cannot be attached to it. Thorough mechanical cleansing of the tail and surrounding parts is a first essential. Before the razor is used, warm water and soap should be applied vigorously for some time, thus softening the hair and removing all scurf. Disinfecting the tail previous to bleeding should never be allowed to degenerate into a mere perfunctory process. During the bleeding operation every effort should be made to prevent the vacuum from being broken, for this admits a stream of air which may be con- PREPARATION OF ANTI-HOG-CHOLERA SERUM 103 taminated, and which, in any event, is sure to hasten coagulation of the blood. We have not found defibrinating during the bleeding process either necessary or desirable. If it is done by shaking the jar into which the blood is flowing, it causes the hog to struggle, thus re- tarding the bleeding process and rendering break- ing of the vacuum imminent ; and if it is done by any device which renders shaking unnecessary during the time the blood is being drawn, com- plete defibrination can be brought about only by shaking the jar after bleeding is discontinued. On the other hand, if the hog is allowed to lie per- fectly quiet, and if moderate and steady traction is applied after the vacuum is established, bleed- ing takes place rapidly, and almost without excep- tion perfect defibrination will be secured if the blood is shaken immediately after bleeding is com- pleted. Individuals differ, but the average hog bleeds best under about fifteen inches of vacuum. Contrary to what might be expected, a more per- fect vacuum than this usually tends to retard bleeding rather than to hasten it. Each hyper is bled once each week during a series of from two to four bleedings, after which it may be rehypered at any time. In rehypering only 21/2 mils of virus per pound body weight are required. Following this second dose of virus a 104 HOG CHOLEKA like series of bleedings takes place, the first oc- curring from seven to ten days subsequent to re- hypering. The final bleeding takes place from the throat in exactly the same manner in which virus pigs are bled, except that the blood is usually drawn into a deep porcelain receptacle, and de- fibrinated by whipping it with a large fork. If inspection does not disqualify, the blood of the hyper, which has been kept separate throughout the two series of bleedings, is admitted to test, and the carcass is placed on the market. Handling serum blood. Immediately after the bleeding process is completed the jar containing the blood is sealed, and then shaken for a few moments to whip out the fibrin. When this proc- ess is completed the jar is placed in ice- water. Later, the fibrin is separated from the fluid by exactly the same process that is employed with virus blood. Here again, the clot-press is detri- mental because it adds superfluous debris to the serum and causes it to be exposed to the air un- necessarily. After the defibrinated blood is strained there is added to it, as a preservative, 10 mils of 5 per cent aqueous solution of carbolic acid for each 90 mils of blood. The product is then placed in storage bottles, labeled, and re- frigerated pending the time when enough has accumulated for a test. In laboratories which do not clarify the serum, PREPARATION OF ANTI-HOG-CHOLERA SERUM 105 the blood of each hyper is stored separately so that if the animal should show on autopsy general- ized tuberculosis or other disqualifying disease, the blood may be discarded. Local conditions must govern these details. In our own laboratory where it is possible to purchase hypers which have not followed cattle and have not been fed raw creamery products, we always mix bleedings, in spite of the fact that we do not clarify the serum. We have never had a hyper show generalized tuberculosis, and in the few instances in which we have found the disease localized, we have used a guinea-pig test to determine the fitness of the serum for market. We believe this test has a wider application than is now accorded it. FINAL PROCESSES IN SERUM PRODUCTION Testing. Irrespective of detail in preparation, the final requirement is that the finished product shall pass a test proving its protective potency under carefully controlled conditions. For this purpose there is drawn a sample from a mixed lot consisting usually of about 100,000 mils of serum. Seven pigs weighing between 45 and 90 pounds each are selected for the official Bureau of Animal Industry test. Temperatures must be normal and all pigs in good physical condition at the time the test begins. Each pig is given 2 mils of hog cholera virus, five of them receiving in addition, 106 HOG CHOLEEA and at the same time, 20 mils each of the sample of serum to be tested. The other two receive no serum, but are employed as controls to determine the virulence of the virus. Daily observations are made and temperatures are recorded as required, preferably once a day. The essential require- ments for a satisfactory test are that both pigs which receive virus only shall sicken during the test period (21 days) and that at least one of them shall sicken between the fourth and seventh days subsequent to injection, and shall before the fif- teenth day suffer from hog cholera in a degree sufficient to cause death. As an additional con- dition, no more than one of the pigs that receive serum and virus shall show visible illness, and in case one should sicken it must be completely re- covered before the twenty-first day following the beginning of the test. Bureau of Animal Industry regulations govern- ing the interpretation of tests will be found in the Appendix. In general, tests are classified accord- ing to results as ' ' satisfactory, " "unsatisfac- tory" or "no test," the latter giving indefinite results. The satisfactory test has already been described; the unsatisfactory test is usually re- ferred to impotent or contaminated serum; re- tests are indicated when the serum-treated pigs or more than one of the virus pigs sicken before the fourth day, when the control pigs do not sicken 107 108 HOG CHOLEEA as is required in a satisfactory test, or when inter- current disease or accident intervenes. Too much stress cannot be placed on the test, for it is here that all technique leading up to com- pletion of the finished product receives its final confirmation. Careful observations are necessary as well as strict interpretations which withhold from use all doubtful serum. Regulations are a valuable guide, but they themselves require skill- ful interpretation, and no exact rules can be laid down which will serve their intended purpose under all circumstances. Is the serum highly po- tent? Is it free from organisms that will injure hogs into which it is injected? When test con- ditions answer both questions definitely in the affirmative, the serum is fit for use. If doubt re- mains it may be retested, and if it has failed to protect healthy pigs in average condition it should be discarded. In our own work we greatly prefer an eight pig test in which two of the serum pigs receive 10 mils each of serum, two 15 mils each, and two others 20 mils each. We believe that these low doses give much more complete information re- garding the potency of the product, thus allowing a greater margin of safety and adding to the con- fidence with which it may be used in the field. Out of the last 45 tests conducted in this manner 37 have passed without incident, intercurrent dis- PREPARATION OF ANTI-HOG-CHOLERA' SERUM 109 ease (heavy ascaris infestation) necessitated three retests which were satisfactory, one 10 mil serum pig died in each of two, one 15 mil pig died in one, and two were wholly unsatisfactory due to low potency. The test pigs ranged in weight be- tween 27 and 105 pounds, the average being 59. It is of advantage to select test pigs from herds in which no immunizing has been done and in which hog cholera has not appeared in recent years. It is well if all pigs in a single test can be litter mates. The pigs should not be subjected to long hauls just before they go on test, and dur- ing the test great care is necessary to prevent overfeeding of the serum pigs at the time when their reaction begins, which is about the time the virus pigs refuse feed entirely. As a routine measure it is a good plan to reduce the feed one- third or one-half on the morning of the fourth day of test, and to feed subsequently so that the serum pigs are kept just a little hungry. It is interesting and highly instructive to ob- serve the progress of a series of tests, and we know that some field workers would be more cau- tious in their vaccinating if this experience could be theirs. It is in this manner that we see results of the battle between protective and destructive forces, and are brought to realize how easy it is for some disturbing factor to turn the tide in favor of destruction. The virus pigs usually show 110 HOG CHOLEBA a temperature near 106° F. on the fourth or fifth day of the test, and this high level is maintained several days. Other symptoms of hog cholera ap- pear a day or two after the temperature curve starts upward. The pigs which receive protective serum in addition to virus also undergo a reaction, which is slightly delayed and very mild as com- pared to that observed in the virus pigs. In some instances no temperature reaction is discernible, but usually readings reach a point between 104° and 105° F., considerable fluctuation between nor- mal and this level being observed. As a rule the casual observer would detect no evidence of a physical reaction, but not infrequently the appe- tite lags just perceptibly for two or three days and in white pigs a slight flush may be observed in the skin. On the whole, all evidence of reaction has usually disappeared from the serum pigs be- fore the tenth day of the test. According to Bureau of Animal Industry regu- lations, serum which protects in doses required in their official test is suitable for use in the field under a dosage label as follows : Sucking pigs 20 mils Pigs, 20 to 40 pounds 30 mils Pigs, 40 to 90 pounds 35 mils Pigs, 90 to 120 pounds 45 mils Pigs, 120 to 150 pounds 55 mils Hogs, 150 to 180 pounds 65 mils Hogs, 180 pounds and over 75 mils PREPARATION OF ANTI-HOG-CHOLERA SERUM 111 Bottling and labeling. After a lot of serum has passed a satisfactory test it remains to place it in bottles of suitable size for shipping. In large laboratories this is done with machines de- signed especially for the purpose ; in smaller ones it is done by placing the serum in a large covered container drained by a tubular outlet on which is fitted a few inches of rubber tubing. This tubing terminates in a small umbrella-shaped aluminum device, the serum flowing through the part repre- senting the handle, and the bottle being protected from dust during the filling process by the part representing the cover. All bottles intended for shipping are sealed and placed in the refrigerator until they are needed. A label should be placed on every bottle of se- rum shipped, and should include : 1. Eelease tag and license number if the labora- tory is being operated under federal license. 2. Name and address of manufacturing firm or institution. 3. Dosage table. 4. Identification mark, which will enable the manufacturer to trace the exact history of any bottle of serum. 5. Return date, or latest date on which the se- rum may safely be used. 6. Brief directions for use and caution regard- ing methods of preservation. 112 HOG CHOLEBA The finished product. It has already been shown that all serum sent out is, or should be, subjected to carefully controlled tests in which it is required to protect laboratory pigs in much smaller doses than would be administered to like animals in the field. The protective defibrinated blood, called anti-hog-cholera serum, is the basic preparation from which all the more or less re- fined products now on the market take origin, and when it is prepared with careful technique it is in the original state a highly effective and safe im- munizing agent. It may or may not be sterile. ' Clear serum is "bloody serum" minus blood corpuscles. It is prepared from the protective defibrinated blood by various combinations of processes which, individually considered, include precipitation of the red blood corpuscles with navy bean extract, centrifuging, and filtering through various materials. Heat, 60° C., for one- half hour, is applied, which kills some contaminat- ing organisms that may be present. An impres- sion seems to prevail that all clear serum is sterile, but this is not true, for it is not necessarily sub- jected to temperatures or other treatment which will kill or remove all living bacteria. The comparative merits of clear and "bloody" serum are the subject of much controversy, but as is true of other things of like nature, individual methods are the deciding factor. Clear serum, PREPARATION OF ANTI-HOG-CHOLERA SERUM 113 if not subsequently diluted may be administered in somewhat smaller doses than can "bloody" serum, it is free from extraneous matter which has no immunizing value, and all other things being equal it is more likely to be sterile. On the other hand it usually becomes cloudy on standing, its keeping qualities and continued potency after heating, so often emphasized, are yet to be fully established, and it is more expensive than the "bloody" serum. "Bloody" serum contains cor- puscles which are of no value in immunizing, and, like the clear serum, if it is not carefully prepared it may also contain excessive numbers of bac- teria. On the other hand it is not subjected to complicated processes which invite error in tech- nique, and it can be prepared much more cheaply, per immunizing unit, than clear serum. Disregarding entirely the form of the finished product, the test, conscientiously applied and skillfully interpreted, is the swine breeder's guar- antee of safety to his herd. Thus either clear or "bloody" serum, carefully prepared, is a safe and effective immunizing agent; neither, carelessly prepared, will produce the results the breeder and his veterinarian have a right to expect. The relative merits of tail-bled and carotid-bled serum have also been the subject of much absurd controversy, for no scientific evidence has ever been submitted to prove one product different 114 HOG CHOLERA from, or superior to, the other. Carotid-bled se- rum is a mere "talking point. " Some laborato- ries situated near stockyards can produce it more cheaply than they can produce the tail-bled prod- uct, and this fact, rather than considerations based on the quality of the product, explains their preference for carotid-bled serum. Both products pass like tests before being released for use. The keeping qualities of anti-hog-cholera serum vary with different lots, and with various methods of preparing and storing. Bureau of Animal Industry regulations place the expiration date at two years from the time the first bleeding in a particular lot takes place, and subject to satis- factory retest at the end of two years, another year may be added. Our own preference is for a shorter period, for in one or two instances we have known serum to fall away in potency before it was two years old. Serum should always be stored in a dark, cool place. According to a limited number of tests conducted by Kernkampf, freezing does not in- jure it, but temperatures below the freezing point are not desirable. A temperature between 40° and 55° F. seems to be most favorable. After the seal on a bottle has been broken and a portion of the serum removed, the remainder should be used in the course of a few days, or discarded. It is always well to open the bottle out of doors, if all PREPARATION OF ANTI-HOG-CHOLERA SERUM 115 the serum contained in it is not required for im- mediate use. The scope and purpose of this book do not allow further detail which might profitably be included in a more inclusive text. In leaving the subject of serum production, let us emphasize again a few essentials which make for clean, potent serum. These include strong vigorous hypers that have been immune to hog cholera a long time before being hypered; a highly virulent strain of virus that will " ripen'* pigs to kill in seven days, or less; scrupulous cleanliness and strict antisepsis in all operations; rapid cooling of all blood im- mediately after it is drawn ; no unnecessary han- dling or exposure of serum during the process of defibrinating and straining; and finally, careful observation of tests, with positive exclusion of doubtful serum. Hog Cholera Virus Hog cholera virus, called by the trade "simul- taneous virus " because it is used in the field in conjunction with protective serum, is produced by giving shoats doses of virus (usually 2 mils each), allowing them to sicken, and drawing their blood while the disease is at its height. This blood is handled in exactly the same manner as hyper- ing virus, differing from this latter product only in that there is added to it as a preservative, 5 116 HOG CHOLEEA mils of 5 per cent aqueous solution of carbolic acid for each 95 mils of blood. The pigs used to pro- duce simultaneous virus must meet the same es- sential requirements as are met by those used to produce hypering virus; that is, they must show ample evidence that they are suffering with acute hog cholera at the time they are bled, and they must be free of all other infectious diseases trans- missible through their blood. Hog cholera virus is sometimes heated at 50° C. for twelve hours before being sent out, in which case a virulence test is necessary before it can be released for field use. In our own work we greatly prefer unheated virus. Keeping qualities. Like protective serum, hog cholera virus must be kept in a dark, cool place. Bureau of Animal Industry regulations allow it to be used not more than sixty days subsequent to the date of drawing, but wherever a thirty-day limit is practicable, we believe it is safer. There are times when an inactive virus may result in as heavy losses as are sometimes charged to impo- tent serum. Labeling. The virus label should include: 1. Eelease tag and license number if the labora- tory is operated under federal license. 2. Name and address of manufacturing firm or institution. 3. Dosage table. PREPARATION OF ANTI-HOG-CHOLERA SERUM 117 4. Identification mark, enabling the manufac- turer to trace the exact history of any bottle of virus. 5. Eeturn date, or latest date on which the virus may safely be used. 6. Directions for storing. 7. Brief directions for using, and cautions to be observed in destroying unused virus. Hog cholera virus is dangerous material. One- half mil or even less will readily kill an ordinary susceptible hog if protective serum is not admin- istered in conjunction with it. Thus hogs given simultaneous treatment in the field actually re- ceive, as a routine measure, a lethal dose of virus. It is really remarkable that this practice results in so little trouble, but potential danger, slight though it is, exists whenever virus is used, and this fact should be well understood both by the veterinarian and his client. Under no circum- stances should virus be used by untrained men. CHAPTER VIII METHODS OF USING ANTI-HOG-CHOLERA SEBUM Confining the animals. We will consider first methods of confining the animals to be treated. To one unaccustomed to handling hogs the task of confining and vaccinating a large herd of swine seems formidable, and not infrequently the diffi- culties presented, although largely imaginary, have led to costly neglect or procrastination. Chasing hogs to catch them is usually futile, it is time consuming, and if double treatment is to be applied, or if the animals are fat, the practice is positively dangerous. Ingenuity is required, and the veterinarian who can use the help and ma- terials at hand to best advantage, enabling him to vaccinate a herd quietly and rapidly, and without exciting the animals, gains much in the confidence of his clients. If the time that vaccinating is to be done is known to veterinarian and client the latter should tempt the animals into pens or small enclosures with feed and fasten them in securely. Bedding should be provided so that the hogs will be clean and dry. In cases of emergency, where this ad- 118 METHODS OF USING ANTI-HOG-CHOLERA SEKUM 119 vance knowledge is lacking hurdles should be used to crowd the animals into the corner of a yard or PLATE 14. Injecting anti-hog-cholera serum in the ham pasture. In all cases in which fences are insecure it is important to mark each animal at the time it is vaccinated, so that if treated and untreated ones 120 HOG CHOLERA should accidentally get together identification will still be possible. Paint, chalk, bluing or tincture of iodin are convenient for this purpose, or if a PLATE 15. Method of holding shoat for injecting serum in axillary space permanent mark is desired, the ear may be notched. Assuming that the animals are fastened in small pens when the veterinarian arrives, confinement of the individual during the process of immuniza- METHODS OF USING ANTI-HOG-CHOLERA SERUM 121 tion is the next step. As a site of injection, one may select the armpit, medial surface of the thigh, or the area immediately behind the ear. The site PLATE 16. An improvised method of holding shoats for immunizing. Injecting serum in axillary space chosen, the size of the animal and individual pref- erences determine the method of holding. If the site is to be the medial surface of the thigh, any 122 HOG CHOLEEA pig weighing less than sixty pounds may be seized by the hind legs and held with the head suspended, belly toward the operator. If the armpit is chosen the pig is suspended by the front legs which are drawn well apart. Shoats weighing more than sixty pounds are confined in a variety of ways. Sometimes they are thrown and held on their backs; sometimes two men suspend them by their hind legs ; at other times it is convenient to incline a V-shaped hog trough against a fence so that it forms an angle of about 45 degrees with the ground. Into this the shoats are placed on their backs, heads downward, and their snouts are allowed to slide under a cleat which extends across it. Perhaps the most serv- iceable method of handling animals of this size is to seize them by the front legs and set them on their haunches with their backs drawn firmly against the legs and body of the man holding them. In this position they are quite helpless and they are easily held as their weight rests entirely on the ground. Shoats thus confined are injected in the armpit. In throwing larger hogs that are to be held on their backs for treatment it is well to seize them by the front leg on the nearest side. A common mistake is to reach under them for the off foreleg. Another convenient and surprisingly easy method of throwing is to seize the tail with the right hand METHODS OF USING ANTI-HOG-CHOLERA SEBUM 123 and the left hind leg with the left, pulling down- ward and to the right on the tail, upward and to the left on the leg. Like the double half -hitch in throwing a bull, this method of throwing hogs is effective, but its manner of action is a mystery. Large hogs are seldom thrown but are confined either by means of a noosed rope which is placed well back in the mouth and tightened around the snout, or with one of the many types of hog-hold- PLATE 17. Convenient hog holder made from % inch gas pipe and flexible clothes wire. It may be disjointed in the middle for convenience in carrying ers. In case a snout-rope is used it should be either 14 or % inches in diameter, and about fif- teen feet long. An eye about % inches in diame- ter is braided in one end, and through this the other end of the rope is passed to make a running noose. Directly around the rope forming the noose is braided a jerk-rope about a foot long. This device renders it possible to release a hog instantly, and saves time, for if it is not used re- leasing the animal sometimes is as difficult as confining it. A large rope tied in any manner to 124 HOG CHOLEKA form a running noose is clumsy to handle, and allows a great many animals to escape. There is a great knack in noosing the snout of a large hog. Assuming that a person is right- PLATE 18. Method of preparing snout rope for confin- ing large hogs. The short "jerk-rope" renders it possible to release the hog instantly. ^4 or % inch Manila rope is used handed he should stand near the center of the pen and start the animal moving around it to the left, at the same time seeking a position at the hog's left shoulder. Holding in readiness a short sec- tion of the noose, and at the same time crowding METHODS OF USING ANTI-HOG-CHOLERA SEBUM 125 the hog suddenly and forcibly against the side of the pen with the right leg, one takes advantage of the fact that the animal opens its mouth to squeal or champ its teeth when its progress is thus momentarily arrested. The noose is slipped into the mouth, drawn backward quickly, and tightened PLATE 19. Method of noosing the snout of hog. The animal is forced suddenly against the gate with the right knee, the noose is thrust into the mouth, drawn behind the canine teeth and tightened around the snout. The free end of the rope is then secured and the animal is tapped on the snout to make it pull backward, for a hog will not stand quietly unless the rope is tight. In this position the site of injection behind the ear is readily available. When a sow and sucking pigs are to 126 HOG CHOLERA be immunized, the sow should be tied and injected first, and released only after the pigs have been vaccinated. Another method of confining large hogs is to connect two pens with a narrow, low chute, which can be closed at both ends. Into this a limited number of hogs are crowded tightly as they pass from one pen to the other, and the operator may reach over the side of the chute and inject the animals behind the ear. This involves some labor in preparation, but it is a rapid method of han- dling, and may be serviceable when a large num- ber of hogs are to be immunized. Quiet hogs may sometimes be injected without resorting to noose or holder as the operation is by no means painful. Methods of Using Serum Preventive vaccination against hog cholera in- volves the use of just two materials; anti-hog- cholera serum, which is protective in nature, and which is prepared from the blood of hogs that are hyperimmune to cholera; and hog cholera virus which is the defibrinated and preserved blood of pigs that are suffering with hog cholera at the time bleeding takes place. With these two ma- terials three methods of immunizing have been developed; serum alone, simultaneous (double, or serum- virus), and follow-up, which is a combina- tion of the two first-named methods. METHODS OF USING AN TI- HOG- CHOLERA SERUM 127 The practicing veterinarian is regularly re- quired to select the method best suited to the conditions he encounters, and he can handle hog cholera with maximum efficiency only when he judiciously chooses and employs the particular method indicated. The selection is based entirely on the effects produced by each method, just as we choose drugs on the basis of their action. When once these effects are well understood, the choice involves no great difficulties. Serum alone method. This consists of deep injection of the required quantity of serum. If the animals thus treated are not infected l with hog cholera immediately before or during the four weeks following serum administration the immu- nity conferred may, with rare exceptions, be de- pended on four weeks. In many individuals it lasts much longer. Swine more than twelve weeks old that receive serum alone and are infected with cholera immediately before immunization, or dur- ing the three or four weeks following, are there- after permanently immune. The effect on pigs less than twelve weeks old is still a matter of con- troversy, but at present we are not safe in depend- 1 Much misunderstanding has arisen because of the loose use of the terms "infected" and "exposed." The first term implies that hog cholera virus sufficient to produce the disease has actually entered the system; the second implies that the animal has been in close contact with virus from any source, but infection may or may not have taken place. Hogs given serum alone and in- fected with hog cholera acquire a permanent immunity; if they are exposed but not actually infected the immunity is temporary. 128 HOG CHOLEKA ing on serum alone plus natural infection to pro- tect young pigs more than four weks. Technique of serum administration. Require- ments. Serum in covered container, or in a bottle fitted with cannula through which it may be drawn; hypodermic needles, and syringe, the lat- ter preferably one of 30 or 40 mil capacity ; anti- septic solution in large container, and scrub-brush, for disinfecting site of injection; antiseptic solu- tion in small container for disinfecting needles and syringe. In field work these are placed conven- iently upon an improvised table consisting usually of a box covered with a clean towel or oilcloth. The pig is confined in the manner already de- scribed, and the site of injection is thoroughly cleansed with the scrub-brush dampened in anti- septic. If syringe and needles have not been pre- viously sterilized, they should now be thoroughly disinfected, after which the required quantity of serum is drawn into the syringe and injected deeply into the tissues. As the needle is with- drawn it is well to pinch the skin to prevent back- ward flow of serum. Massage is now applied if required, the site of injection is again dampened in antiseptic, and the pig is released. Choice of the site of injection is governed by the size, condition and intended use of the animal, by the method of confining, and by individual preferences. All other things being equal we pre- METHODS OF USING ANTI-HOG-CHOLERA SEBUM 129 fer the armpit because the skin covering it is usually clean, the serum enters the tissues freely, and with each step the animal takes, massage is automatically applied. Very young pigs are most PLATE 20. Injecting serum behind the ear. The needle is thrust deeply into the loose areolar tissues, and very little force is required to expel its contents conveniently confined for injecting in the ham. Heavy hogs, especially pregnant sows, are almost always injected behind the ear, because it is safer and more convenient to confine them standing. Hogs nearly ready for market should not be in- 130 HOG CHOLERA jected in the ham, and young pigs and shoats are not injected behind the ear. Sometimes serum is administered in the flank, or in the loose tissues immediately back of the elbow, but we believe neither practice has much to recommend it. Rapid and complete absorption of serum is greatly to be desired, because it gives the highest and most prompt immunizing effect, and tends to prevent abscess formation. Some will inject no more than 20 mils of serum in a place, believing that a greater quantity will be absorbed but slowly, but it is the placing and distribution of the dose, much more than its size, that govern ab- sorption. In real small pigs it is well to divide the dose, and whenever possible the practice may be followed in older animals. In injecting young pigs the parts that receive the serum should be kneaded gently after the needle is withdrawn; in larger animals the needle should be thrust deeply into the loose tissues immediately behind the ear, and after the injection is completed the ear should be drawn forward and vigorous massage applied in order to distribute the dose. Serum injected immediately beneath the skin, forming a distinct welt, absorbs but slowly, and when it fails to spread in the deeper tissues, as evidenced by un- due pressure required in making the injection, rapid absorption cannot be expected. A syringe METHODS OF USING ANTI-HOG-CHOLERA SEBUM 131 which operates easily and requires uniform pres- sure on the plunger should always be selected. Cleaning and disinfecting the site of injection are processes frequently neglected, because the hog is proverbially difficult to infect. He can be infected though, as some have found to their sor- row. If hogs are at pasture or in clean, dry, well- bedded pens, cleaning is not difficult. Some sim- ply paint the skin with tincture of iodin, and this answers well when the site of injection is both dry and clean, but tincture of iodin is not suitable for use on wet surfaces. We have found nothing better than a good coal-tar disinfectant applied with a stiff scrub-brush, for this removes all dirt and scurf, in addition to furnishing the desired antiseptic action. If pigs are unusually dirty the site of injection should first be cleaned with warm soapsuds. Good technique includes thorough me- chanical cleansing, and nothing else will take its place. Dosage of serum. The best rule is to give at least as much serum as the label requires. Serum varies widely in immunizing units per mil, and although the margin^ of safety — the increase of the field dose over the laboratory test dose — ob- served in individual laboratories is not the same, doses recommended in any particular laboratory are, in a very general way, determined by its indi- 132 HOG CHOLERA vidual methods of preparing and testing. Dosage is based on weight, and one not accustomed to estimating weights of hogs should weigh one or more before beginning work, for a common and disastrous error is to estimate far too low, and to give correspondingly small doses of serum. Not infrequently we have known weights to be estimated at less than half what they actually were. We believe a common error in dosing, and one for which labels are frequently responsible, consists of giving all hogs above a certain weight a fixed quantity of serum. Thus on one label we read: "Hogs 180 pounds and over, 75 mils," A hog weighing 180 pounds may properly receive 75 mils of average serum, but one weighing 500 pounds will not be adequately protected by that quantity. Under all conditions under which it is known or suspected that the hogs have resistance below the average, it is a wise precaution to in- crease the dose measurably. In badly infected herds it should be doubled. If serum is carefully administered, with due precautions regarding rapid absorption, it is prac- tically impossible to overdose, and there is no dis- ease or condition of swine, so far as we know, that even an unnecessarily large dose of serum alone will affect unfavorably. Thus in case of suspected hog cholera, in which the diagnosis cannot be clearly established, it may, and should be, admin- METHODS OF USING ANTI-HOG-CHOLEfcA SERUM 133 istered ; and in case deviation from the dose table seems desirable, a quantity unnecessarily large is preferable to one dangerously small. Therapeutic value of serum alone. Serum is employed almost entirely as a preventive of hog cholera, but it possesses some therapeutic value when used in generous doses early in the course of the disease. Herein lies the reason for in- creased doses in badly infected herds — many ani- mals apparently well are really in the first stages of hog cholera. Ordinarily we do not regard treating hogs visibly sick with cholera as a profit- able venture, but when the disease appears in mild form, or when the animals are adults or of excep- tional value, we are more than repaid for our efforts to save them. Double doses of serum are recommended under such circumstances, and or- dinary doses may follow at intervals of from three to seven days, as the condition of the animal re- quires. Good nursing as an adjunct to serum treatment is of the utmost value. A plentiful supply of fresh water should be furnished, to which may be added a saline purgative when there is constipation. The diet should be severely restricted, and under no circumstances should unconsumed food be kept before the animal. Warm milk alone is an excel- lent diet for hogs suffering with cholera. Dangers and after-effects of serum alone im- 134 HOG CHOLEKA munization. Occasionally rough handling during the process of vaccinating will injure an animal, but this is not to be charged to the effect of serum. Sometimes, especially in very young pigs, a tem- porary stiffness or lameness exists for a day or two following treatment, but this is exceptional, and usually it is of little consequence. Large quantities of cold serum, especially when the dose is not well distributed, sometimes cause this trouble in an aggravated form. The obvious pre- cautions are to use due care in injecting, and to warm serum that is to be administered to young pigs in cold weather. A temperature approaching blood heat is desirable, and may be secured by placing the bottles in warm water. Very exceptionally there is observed, immedi- ately following serum administration, a rapidly spreading local infection often involving an entire quarter and encroaching on other parts. There is acute lameness in the affected quarter. The area involved is either doughy in consistency, or else gas formation is evident, and under both con- ditions there is pronounced edema. The skin usually assumes a purple hue. As a rule, animals thus affected die in a short time. We have seen but a limited number of such cases, and with one exception, all could be traced to gross carelessness in technique, or to working conditions which ren- dered even average technique impossible. We METHODS OF USING ANTI-HOG-CHOLEKA SEEUM 135 have never seen a considerable number of animals in one herd thus affected. Abscesses follow serum administration infre- quently, and like the rapidly terminating type of infection just described, they are usually asso- ciated with faulty technique or conditions below the average as far as sanitary surroundings of the animals are concerned. They occur most fre- quently in poorly nourished, weak animals, but are not always thus limited, nor is it possible in all cases to ascribe them to bad technique. The bacterial flora of the particular surroundings in which the immunizing is done seems to play an im- portant part, but even this factor may be con- trolled to a great extent by the free use of disin- fectant. Dust contamination of serum and instru- ments also favors abscess formation, and for this reason one should work out of doors whenever possible. Failure to distribute the dose of serum thoroughly sometimes results in local inflamma- tion, leading to abscess formation. Abscesses are rare when the serum is not contaminated, when care is used in administering it, and when the treated animals are in reasonably clean quarters. Vaccination abscesses usually encapsulate and form slowly, and although they sometimes reach a considerable size and retard the growth of the animal to some extent, they rarely threaten its life or cause general symptoms of disease. If 136 HOG CHOLERA they occur in the hams of hogs ready for market they are highly objectionable, as they cause con- demnation of the entire quarter in which they are located. The handling of vaccination abscesses consists of opening them when the first evidence of fluctuation appears, pressing out the thick, greenish-yellow pus which they usually contain, and irrigating the sac with weak antiseptic solu- tion. In opening, the incision should be made with due regard for continuous drainage. Considerable space has been devoted to these untoward results which sometimes follow serum administration, but on the whole they are uncom- mon when reasonably good technique is employed. One who is careful will immunize hundreds and even thousands of hogs without encountering difficulties of this kind, but it is well to know that they sometimes occur, and to understand the im- portance of seemingly trifling influences that operate to cause or prevent them. Summary of action of serum alone. 1. Produces in hogs not infected with cholera near the time of its administration a passive im- munity lasting about four weeks. 2. Produces active and permanent immunity in swine more than twelve weeks old that are defi- nitely infected with cholera immediately before immunization, or during the three or four weeks following it. METHODS OF USING ANTI-HOG-CHOLERA SERUM 137 3. Produces an active and permanent immunity in many pigs less than twelve weeks old which are definitely infected with cholera near the time of treatment, but cannot be depended on to produce permanent immunity in all young pigs. 4. Does not affect other diseases unfavorably, and if it is carefully administered, untoward re- sults following its use are practically negligible. Indications for serum alone. 1. In seemingly well and exposed animals in in- fected herds. 2. In all cases in which a four-week immunity will meet the requirements. (Show hogs under some circumstances, those near the end of the fattening period, breeding animals crated for shipping.) 3. In all cases in which immediate protection is required and simultaneous treatment cannot be safely administered. (Sows near farrowing time, weak unthrifty animals temporarily threatened with hog cholera.) See also follow-up treatment. C ontra-indications for serum alone. Serum alone is contra-indicated when the following con- ditions coexist in the same herd or animal. 1. A permanent immunity is desired. 2. Hog cholera infection does not exist. 3. Simultaneous treatment may safely be ad- ministered. Simultaneous or double treatment. This 138 HOG CHOLERA method consists of giving serum in exactly the same manner as has already been described, and of administering at the same time, and with a separate syringe, the required dose of hog cholera virus. Usually the dose of serum is given in one of the sites of injection already mentioned, and the virus at the corresponding point on the oppo- site side. The technique of administering virus does not differ from that employed with serum, except that special care is required in disinfecting the site of injection after the needle is removed. Also the dose of virus is so small that massage is not required. No virus should be allowed to drop on the ground, and all that is not used should be burned. Simultaneous treatment possesses the great ad- vantage of producing a permanent immunity in all swine that are more than twelve weeks old, and in many of those that are younger. On the other hand it involves the use of a lethal dose of hog cholera virus, thus producing certain sequelae and adding specific dangers that are not associated with serum alone treatment. Dosage of serum and virus. The same princi- ples that apply to dosage of serum administered alone, apply when it is given with virus. We give at least as much serum as the label indicates, in- creasing the dose when we are compelled to ad- minister simultaneous treatment to hogs below METHODS OF USING ANTI-HOG-CHOLERA SERUM 139 average in resistance. In using virus the label is likewise our guide. Although in giving simultane- ous treatment to hogs we regularly administer a lethal dose of virus, we should not let that fact tempt us to decrease the quantity. Too much stress has been laid on carefully graded doses of virus and on the necessity for balancing virus and serum doses. One mil of virus will kill almost as regularly and quickly as three, and an ordinary dose of serum will protect against either quantity. The dose of serum is not governed by the quantity of virus, but by the potency of the serum, which is reflected on the label, and by the size and con- dition of the hog. Thus, if circumstances compel us to give simultaneous treatment to hogs below average in resistance, we increase the dose of serum, but leave the virus dose unchanged. The primary aim is to give enough virus to infect, and enough serum to protect against an infecting dose. In our own field work we never give less than one mil of virus nor more than two mils, our prefer- ence being for a dose approaching the latter figure in all swine weighing more than seventy-five pounds. After-effects and dangers of simultaneous treat- ment. A reaction, very slight in the vast ma- jority of cases, but severe in others, usually follows simultaneous treatment. In effect, the animals go through an attack of hog cholera which 140 HOG CHOLERA is so light that symptoms do not appear, but if temperatures are recorded the curve will usually show slight elevation and more or less fluctuation between the fifth and twelfth days following immu- nization. Under unfavorable conditions the reac- tion becomes relatively more severe, and symp- toms of hog cholera may appear. If these are slight, complete recovery will take place; if they are severe, they threaten the life of the animal; and if it dies its death is due to hog cholera just as truly as it would be if no serum were adminis- tered^. Sickness and deaths due to hog cholera following simultaneous treatment are termed "breaks" or "vaccination cholera." If the trou- ble appears during the first three weeks following treatment it is called a "serum break" the suppo- sition being that the serum is impotent and allows the virus to kill the animal ; if it appears after a longer time it is termed a "virus break, ' ' the effect being ascribed to the fact that inert virus has been administered and the serum produces only a tem- porary immunity, which, as it disappears, leaves the herd again susceptible. In reality, ' ' serum breaks ' ' are due to a variety of causes, among which are impotent serum, faulty technique in vaccinating, insufficient doses of serum, and, in addition, any influence whatso- ever that temporarily lowers the resistance of the animals during the two or three weeks subsequent METHODS OF USING ANTI-HOG-CHOLERA SERUM 141 to vaccination. Most important among these may be mentioned shipping, weaning, castrating, heavy ascaris infestation in which the gall ducts are filled with the parasites, overheating incident to handling during immunization, severe exposure in cold rains during the reaction period, injudicious feeding during that time, and general unthrifti- ness due to any cause. These are not imaginary influences that may cause " breaks," but are real influences that do cause them, and while they may be repeatedly ignored without dire consequences, the tendency is to ignore them once too often. The practicing veterinarian is helpless in re- gard to the potency of the serum he uses. He has no opportunity to test it, and must therefore ac- cept it on faith. His safest plan is to secure it only from the most reliable sources. Of course if the virus used is up to standard, and the serum is impotent the hogs that receive the two simultane- ously will probably die, and no veterinarian who has had this result follow his work will soon for- get it. It is well to remember, though, that impo- tent serum is just one of many causes of so-called " serum breaks" and that the remainder of these causes are for the most part controlled by the practitioner or breeder. There is a triple respon- sibility associated with all simultaneous treat- ment, and neither serum producer, veterinarian 142 HOG CHOLEBA nor breeder should throw stones until he is sure he is not living in a glass house. Shipping hogs immediately after simultaneous treatment has been administered, or worse still, holding them three or four days and then shipping them so that they will be on the road at the time the reaction following treatment is in progress, is a fruitful cause of serum "breaks." We are aware that this practice is stoutly defended by many, principally by those who administer the treatment in stockyards, see the hogs loaded in cars, and never see them again. The practice is not defended by veterinarians who are on the re- ceiving end of the line, for it is a well-known fact that "serum breaks " often occur soon after these hogs reach the farms on which they are to be fattened, and it is fortunate indeed if hog cholera is not thus transmitted to other herds in the vi- cinity. This method of handling hogs may be necessary under present conditions, even if it must carry with it the risks we have mentioned, but granting that it is necessary, let us at least recog- nize the dangers in their true proportions, and work toward a better method of handling feeding hogs. Lowered resistance due to shipping accounts for many of these "breaks," yet the tendency is to charge them to impotent serum. The best se- rum that can be manufactured will not protect all METHODS OF USING A NTI- HOG- CHOLERA SERUM 143 animals thus handled, but the fact that many lots of hogs will endure it, leads some to think that all ought to do so. Individual differences exist, and while they are not always obvious, the lots that "break" more often consist of hogs that have been held in stockyards a long time, those badly infested with parasites, or suffering with respira- tory diseases. Distances traveled to and from the stockyards, and the degree of crowding of the cars are also potent factors in determining the hazards of shipping simultaneously treated hogs. Hogs are not fit subjects for simultaneous treat- ment just as they are unloaded from long railway journeys. It is best to give these animals serum alone at this time, and simultaneous treatment two or three weeks later. This is the follow-up treatment which we have already mentioned, and which will be considered separately in this chapter. In farm hogs, weaning, castrating, ringing, and the absurd practice of knocking "black teeth" out of all pigs may operate individually or collec- tively to lower resistance and render simultaneous treatment dangerous. Due to pressure of other work pigs are frequently neglected several weeks, then suddenly there is a desire to do all of these things, and immunize, at the same time, in order to avoid handling the animals more than once. The wonder is that pigs will frequently, even usu- 144 HOG CHOLERA ally, survive the ordeal, but exceptions prove the rule — and embarrass the veterinarian. In several instances we have known men to castrate pigs dur- ing the week following simultaneous treatment. In some of these a number of the castrated pigs died, while the female pigs, which remained as checks, survived, thus furnishing excellent but rather involuntary and costly experiments. Pigs are best castrated as sucklings, but in any event, it is well to separate castrating and simultaneous treatment at least two or three weeks. Ascarids may exist in the intestine in large numbers without appreciably lowering the resist- ance of simultaneously treated pigs, but if the parasites enter and occlude the gall duct, the in- fested hog shows a remarkable intolerance for virus. We have observed this intolerance again and again both in test pigs and in the field. Prac- titioners cannot always avoid trouble due to as- carids, for granting that they know the parasites exist in a herd, it is not always possible to deter- mine their location in the individual, and often it is not safe to delay treatment. Severe jaundice in pigs is usually due to ascarids in the gall-duct, and its presence, easily observed in white pigs, should suggest caution. Overfeeding is injurious to pigs passing through the reaction following simultaneous treatment. Any one who has observed serum tests knows METHODS OF USING ANTI-HOG-CHOLERA SERUM 145 that. Often there is no change in the appetite during this time, but if a few animals in a lot eat scantily, the others gorge themselves on the sur- plus thus rendered available, and a period of dis- tress or dullness follows, during which the virus may get in its work. A simple rule is to feed so that the animals remain just a little hungry after each meal, and to be prepared for a slight lagging in appetite between the fifth and twelfth days fol- lowing treatment. Methods of preventing ' i serum breaks ' ' are ob- vious when the causes of these " breaks " are un- derstood. Full doses of potent serum adminis- tered with due regard for rapid absorption, and proper caution in regard to treating hogs below average in resistance are the two essential con- siderations. Handling "serum breaks" involves first of all informing the owner of the animals, before serum is administered, that such "breaks" are possible but by no means probable, and asking him to ob- serve the herd carefully and report any sickness that may appear during the three weeks following treatment. Should a "break" occur prompt measures are required. If only two or three hogs out of a herd of considerable size appear dull, and if these have sickened later than the twelfth or fourteenth day following vaccination, it is well to take temperatures on several animals in the herd. 146 HOG CHOLEEA If the temperatures vary between normal and a little above 104° F. and if there is no visible dull- ness, serum alone may be given to the sick ani- mals only; but if sickness appears before the tenth day, if several hogs are dull, or if a number of them show temperatures near 106° F. the entire herd should receive full doses of serum alone without delay. Most "breaks," taken in time, can be checked. Abortion in sows has been caused by simultane- ous treatment, but it is rather unusual, and occurs most frequently during "breaks" due to the causes we have mentioned. Sows near farrowing time certainly should not receive serum and virus, but when they are in the early period of gestation we are frequently compelled to assume the slight risks as a necessary evil. Stunting may result from simultaneous treat- ment, and we are told that one of America 's most famous pure-bred breeders had his herd ruined by unthriftiness following vaccination. We do not know the particulars, but we do know that such consequences need not follow simultaneous treat- ment judiciously administered, and we know that hundreds of pure-bred breeders maintain fine herds immune, and are satisfied. We have al- ready enumerated a few of the factors which cause "breaks." Any one of these may cause death, or falling just short of such a result, stunt the ani- METHODS OF USING ANTI-HOG-CHOLERA SEKUM 147 mal. Thus it is the abuse of simultaneous treat- ment rather than its use which incriminates it. Elimination of hog cholera virus in the excre- tions of simultaneously treated pigs sometimes takes place for a few days during the resulting reaction. There was a time when this fact was denied, but no person experienced in handling hog cholera would seriously question it to-day. Beac- tions vary between one extreme in which no tem- perature elevation is recorded, and the other rather unusual one in which death takes place. In the first instance virus elimination is rare, but as the latter extreme is approached, it is the rule. Most hogs do not eliminate infectious material, but the exceptions to the rule are so numerous that it is not safe to keep susceptible animals with those that receive simultaneous treatment. Because of the danger of virus elimination, a period of quarantine is usually imposed on simul- taneously treated hogs. The duration of this quarantine is prescribed by law in most states, the usual time varying between twenty-one and thirty days, with extension in case "vaccination chol- era" appears. Hogs that have shown no physical evidence of disease are very rarely eliminating virus at the end of twenty-one days following serum- virus immunization. " Virus breaks " are not manifest until several weeks following simultaneous treatment, and they 148 HOG CHOLEKA are due to inert virus, insufficient doses, and, very probably, to giving simultaneous treatment to pigs too young. If virus is inert infection is not produced, active immunity is not established, and if hogs chance to be exposed to cholera after the passive immunity due to the serum has disap- peared, they readily contract the disease. If a pig more than twelve weeks old receives a full dose of virulent virus as a part of simultaneous treatment and remains well during the following four weeks, his immunity to cholera may be ac- cepted as a fact ; if a herd that is given simultane- ous treatment passes the first four weeks without incident and later " breaks " with hog cholera, we may safely assume that inert virus was used, or that doses ridiculously low were administered. Sometimes inert virus is sent out with impotent serum that will protect against no other kind; sometimes virus is used too long after being drawn; and if it is heated — we do not believe it should be — there is some danger of killing it. Prevention of " virus breaks," when one under- stands their causes, is simple. Provided one treats pigs more than twelve weeks old, a full dose of virulent virus in conjunction with the serum used in simultaneous treatment is all that is re- quired. A breeder who is familiar with the bene- fits and hazards of simultaneous treatment will not be greatly disturbed if a shoat or two should METHODS OF USING ANTI-HOG-CHOLERA SEBUM 149 die of "vaccination cholera " when he has his herd immunized; he may even view a more serious "serum break " complacently, but if his swine re- ceive simultaneous treatment as shoats and die of hog cholera when they are about ready for market, he has a real grievance, which he will be slow to forget. It is fully as important that virus shall be virulent as it is that serum shall be potent. "Hemorrhagic septicemia" forms a convenient and altogether too common alibi for both ' ' serum breaks " and "virus breaks." If either occurs (and disease which is really hog cholera is called "hemorrhagic septicemia"), this automatically absolves from all blame the serum producer who sells impotent serum or inert virus ; it excuses the man who abuses the products in administering them, as well as the breeder who subjects his ani- mals to improper care during the resulting reac- tion. The only defect in such an alibi is that it does not save the hogs or tell us what really kills them. When hogs kept under average farm con- ditions receive simultaneous treatment and any considerable number of them develop febrile dis- ease during the following three weeks, unless a cause other than "hemorrhagic septicemia" is obvious the chances are ten to one that the primary cause of the disease is hog cholera virus. Under such conditions no other cause can be accepted unless negative filtration experiments, requiring 150 HOG CHOLERA about ten days, are carried out. The field man who represents a laboratory which sells question- able serum, and who pronounces such " breaks" "hemorrhagic septicemia" on information ob- tained from a few autopsies or a brief bacterio- logical examination, must, in mercy, be called ignorant, or else his honesty must be questioned. Most "breaks" can be prevented, but some cannot. Let us prevent those we can, and call the others hog cholera. That is what they are. Under conditions existing in the United States during the last decade simultaneous treatment has been a great boon to the swine industry; it has saved hogs worth millions of dollars ; it has made it possible for any breeder who will, to banish fear that hog cholera will destroy his herd. But in spite of these facts it is not perfect in its opera- tion; it is sometimes instrumental in spreading the disease it is intended to check ; it involves some dangers. These are best avoided when their causes are fully understood ; best combated when they are frankly admitted to exist. Forewarned is forearmed. Any veterinarian who contemplates using simultaneous treatment in a client's herd should tell him that it involves a little danger; that the herd must be carefully handled for about three weeks; that if a " break" should occur it must be reported promptly, and that under no circumstances are susceptible hogs METHODS OF USING ANTI-HOG-CHOLERA SERUM 151 to come in contact with vaccinated ones during the four weeks following treatment. It is some- times difficult to mention these things, without causing the dangers to be exaggerated in a client 's mind, and some breeders will decide not to take risks which they would readily assume could they know how slight they really are. Nevertheless a veterinarian's first duty is to protect his client, and he must protect himself if he is to remain in practice. The man who glibly advises that there is "no danger " following his vaccinating is not doing either. Summary of action of simultaneous treatment. 1. Produces an active permanent immunity in all hogs more than twelve weeks of age. 2. Produces active immunity in some suckling pigs, passive immunity in others. 3. Usually produces a very mild reaction begin- ning about five days following treatment, and last- ing less than seven days. 4. In hogs with low resistance,1 sometimes pro- duces a severe reaction which exceptionally ter- minates in death. 5. Causes some hogs to eliminate hog cholera virus in their excretions during the time the reac- tion is in progress. 1 The terms ' ' resistance ' ' and ' ' condition ' ' should not be con- fused. The former, as used here, applies to the state of the ani- mal's natural defenses against disease, and is determined by the history, as well as by the appearance of the animal. "Condition" 152 HOG CHOLEEA 6. May cause abortion in pregnant sows, and may stunt pigs if they are treated while their re- sistance is low. Simultaneous treatment is indicated in herds where hog cholera virus is almost sure to find its way sooner or later, but where actual infection of the herd may be delayed several weeks or months. Such conditions exist: 1. In sound herds on infected farms. 2. In other herds immediately threatened with cholera. 3. In some show hogs. See " handling show hogs" in Chapter IX. 4. On farms on which hog cholera has appeared periodically. 5. In very large herds in which there is con- stant exchange of animals. 6. In garbage-fed herds. Simultaneous treatment is contra-indicated: 1. When it cannot be applied by experienced men. 2. When the entire herd cannot be immunized. (Some may, if necessary, receive serum alone, but none must be left susceptible.) applies more specifically to the degree and quality of flesh an animal carries, as well as to the appearance of the coat, and is determined, in hogs, principally by inspection. Fat hogs recently shipped or fat sows that have recently farrowed, though in good condition, will not tolerate simultaneous treatment nearly as well as ordinary farm hogs in very moderate flesh. The ' ' resistance ' ' of the latter is higher, although their " condition ' ' is lower. METHODS OF USING ANTI-HOG-CHOLERA SEBUM 153 3. When the treated herd cannot be properly segregated. 4. For sucking pigs as a routine measure. (In- formation still incomplete on this point.) 5. For sows about to farrow, or for those nurs- ing young litters. 6. In badly infected herds. 7. In animals with low resistance due to ship- ping, weaning, castrating and other influences. 8. In all circumstances in which serum alone will be equally effective. Follow-up treatment. This consists of giving serum alone and following it in a few weeks, usu- ally less than four, with simultaneous treatment. It has been called "double treatment " by some, but according to usage which has now become fixed, the terms " double treatment" and "simul- taneous treatment " are applied interchangeably to serum-virus administration. It therefore seems desirable to apply to serum alone followed by simultaneous treatment, the separate, distinct and self-explanatory term, "follow-up treatment. " Follow-up vaccination is safer than simultane- ous treatment, it can be applied under circum- stances which practically forbid the use of the latter method, and the final result is the same — a permanent immunity is established. There are those who believe that the passive immunity pro- duced by the dose of serum alone prevents the re- 154 HOG CHOLERA action and consequent permanent immunity due to subsequent serum-virus treatment. The im- pression seems to prevail that there is just one way to immunize a hog permanently, and that is to give him simultaneous treatment as a first and only measure. Various troubles following follow- up treatment have been cited as proof of this theory, but we have never investigated a case in which there was the least evidence that the system was fundamentally at fault. The trouble has been in its application. In applying the follow-up system, there is a marked tendency for the veterinarian to give the dose of serum alone and to neglect for too long a time to follow it with simultaneous treatment. There is no danger in this unless the pigs happen to be exposed to cholera after the passive immu- nity due to the dose of serum has disappeared, but too often just that very thing takes place. The owner of the animals derives a false sense of se- curity from the fact that serum has been adminis- tered, and hence does not report the sickness as promptly as he otherwise would. The final result is that when hog cholera is well started in the herd, the veterinarian receives an urgent call to give serum and virus as the final installment of the follow-up treatment. Heavy losses inevitably follow, and the entire system is condemned. It should always be remembered that serum alone METHODS OF USING ANTI-HOG-CHOLERA SERUM 155 cannot be depended on to protect more than four weeks. ' ' Virus breaks" are no more likely to occur when follow-up treatment is administered than they are following simultaneous treatment, and, as with the latter method, their prevention con- sists wholly of giving full doses of virulent virus, and using due care not to treat pigs too young. When these precautions are observed, we can vouch for the fact that follow-up treatment pro- duces a permanent immunity. We have used it since 1912 in maintaining many immune herds, usually administering the final dose, simultaneous treatment, when the pigs were about twelve weeks old. We have not had a " virus break" during the nine years the system has been employed; that is, no pigs that survived the immediate reac- tion following the final serum-virus treatment sub- sequently developed hog cholera. It is our custom to select hypers from these herds, and so far none of them have developed hog cholera as a result of hyperimmunization. In the East many veteri- narians use the follow-up system in maintaining herds immune to cholera, and " virus breaks" are not common. Experimentally we have tested the effects of giving follow-up treatment using various inter- vals between the time of administering serum alone and that of administering serum and virus, 156 HOG CHOLERA and trying to smother the action of virus by large and repeated doses of serum alone previous to simultaneous treatment. In no case have we ob- tained evidence to justify even a suspicion that follow-up treatment does not produce permanent immunity, and we know of no experimental work that contradicts these results. The factor of greater safety cannot well be questioned, although it is seldom that hogs with average resistance require follow-up treatment. Simultaneous immunization produces the same re- sult, and is cheaper. But if exceedingly valuable animals are to be immunized, one cannot go amiss in giving a dose of serum alone and following it in a week or two with simultaneous treatment. If the first dose of serum is in the system, already absorbed, when the second dose is given with virus, there can be no question that the hazards are reduced. Exact comparisons of the safety of simultaneous and follow-up treatment are difficult to make, because under ordinary conditions both are nearly 100 per cent effective. We have seen follow-up treatment used in immunizing cattle against rinderpest with losses running less than 5 per cent when simultaneous treatment with the same serum and virus caused such heavy losses as to forbid its use altogether. We do not care to generalize too far on this point, but the princi- ples employed in preparing and using the two se- METHODS OF USING ANTI-HOG-CHOLERA SERUM 157 rums are the same, and we offer the observation for what it is worth. Follow-up treatment is indicated: 1. For very valuable hogs where the greatest possible safety is required. 2. When the following conditions coexist in the same animal or herd : A. Immediate protection is imperative. B. Ultimate permanent immunity is desired. C. Conditions render immediate simultaneous treatment dangerous. Follow-up treatment is contra-indicated in all cases in which it appears 'that serum alone or si- multaneous treatment will be equally effective. It is in immunizing hogs with resistance obvi- ously below normal, and in maintaining immune herds under somewhat adverse conditions that follow-up treatment renders greatest service. In practice, especially in the East, we constantly en- counter the three conditions we have enumerated above, and follow-up immunization relieves us from the necessity of choosing between serum alone which will not produce a permanent immu- nity, and simultaneous treatment which is posi- tively dangerous at the time when immediate pro- tection is required. In a succeeding chapter the adaptations of follow-up treatment will receive further attention in connection with specific con- ditions which we meet in the field. CHAPTER IX HANDLING HOG CHOLERA IN THE FIELD HANDLING hog cholera in the field requires ap- plication of the principles that have been outlined in preceding chapters. In this chapter our plan is to assume the existence of certain actual con- ditions which the practitioner frequently meets in the field, and to suggest methods of handling suited to these conditions. "We know that in doing this we may invite criticism, for methods of han- dling hogs are so widely different in various parts of the country that one cannot supply details that will apply everywhere. In some parts of the South, for instance, where hogs are allowed almost unlimited range, where predatory animals are common, where hog cholera is prevalent, and where a few breeders use simul- taneous treatment regularly, others must protect their hogs in the same manner, or lose them. In certain sections of the corn-belt hog cholera is prevalent to such a degree that it is the part of wisdom for practically all breeders to maintain immune herds. In the East, where hogs are rather closely confined, where they are raised in limited 158 HANDLING HOG CHOLEEA IN THE FIELD 159 numbers, where hog cholera is not common and its spread is not rapid, most herds do not require immunization. Moreover, in the corn-belt where hog raising is a business, methods of swine hus- bandry are relatively much better than they are in sections in which it is a mere adjunct to other farming operations. The average corn-belt breeder has had more or less experience with hog cholera, he knows what it means to have it sweep unchecked through his herd, and he is not in- clined to be dissatisfied with measures that will check it, even though these measures may not always be perfect in their operation. On the other hand, the Eastern breeder whose herd we are called on to handle very often is having his first experience with the disease, he is inclined to be skeptical as to the merits of protective serum, and to doubt its value if he loses a few animals after it has been administered. Frequently also, the herd is found in unthrifty condition due to poor meth- ods of swine husbandry and heavy parasitic in- festation. Virus cannot be used as freely in such surroundings as it can under circumstances where its effects will be more correctly judged. Despite these differences, though, and despite the fact that methods of swine husbandry have a direct and important bearing on the handling of disease, the principle holds that hog cholera is hog cholera the country over, and not, as some 160 HOG CHOLERA would have us believe, different according to the section of the country in which we chance to find it. The differences we observe in various parts of the country are due principally to prevailing sec- ondary invaders, as well as to variation in viru- lence of the hog cholera virus itself, for they are observed also in comparing individual herds or outbreaks in any one section. While we must accept all these variations and allow for them, the underlying principles em- ployed in handling hog cholera remain unchanged, and it is desirable and necessary in a treatise of this kind to suggest definite working plans, leaving the reader to alter or supply detail as individual cases warrant. We are moved to do this because we have seen young graduates of veterinary col- leges who had had good instruction and whose technique in administering serum left little to be desired — we have seen some of these men practi- cally helpless in the presence of outbreaks of cholera which presented disturbing but not un- usual features. Likewise men who are accus- tomed to the routine of vaccinating thousands of stockyard hogs are sometimes confused when they are called on to accept the conditions they meet on the average farm, to prescribe treatment for a mixed lot of swine, and guide the breeder away from future trouble. Mere knowledge of how to vaccinate hogs does not equip one to handle hog HANDLING HOG CHOLERA IN THE FIELD 161 cholera; diagnosis, when and whether to vacci- nate, the method to use, and the subsequent han- dling of the herd all enter into the problem. Handling .the cholera infected herd. Let us assume, as a working basis, that a herd consisting originally of one hundred ordinary shoats, in good condition, is infected with hog cholera; ten have died, ten are visibly sick, and there is no evidence of secondary infection; there are no other hogs on the farm, and the shoats are in a pasture con- taining several acres; the owner has had hog cholera in his herd in previous years, and knows the results that may reasonably be expected from preventive measures. This represents the sim- plest situation we are called on to cope with in handling hog cholera in the field. Three methods of handling are open to us : 1. Give generous doses of serum alone to all animals that are not exceedingly weak. 2. Give simultaneous treatment to all seemingly well animals, and double doses of serum alone to those that are visibly sick, and not obviously near death. 3. Give serum alone in full doses to all ani- mals that are apparently well, in double doses to those that are sick and have a chance to recover, and follow this in three weeks with simultaneous treatment for all animals that were not visibly sick at the time of the first treatment. In other 162 HOG CHOLERA words, give serum alone to the sick animals, fol- low-up treatment to those that are apparently well. Regardless of the method selected, we must proceed promptly with the one that becomes our final choice, and we must take immediate precau- tions to prevent spread of the disease to other herds. Method number one may prove highly satisfac- tory in some cases of this kind, but it is open to the serious objection that it may not produce per- manent immunity in all the animals. In the indi- vidual, serum alone plus hog cholera infection produces permanent immunity, but in a herd of this kind, although all the animals are exposed, some may not become infected in time to secure this result, because hog cholera does not always spread rapidly through herds that are at pasture or in other large runs. Let us select, as an instance, one shoat in the herd and assume that the animal has received serum alone to-day. If in the course of the next three or four weeks — the usual duration of immu- nity due to serum alone — it chances to take up virus sufficient to infect, it will undergo a reaction and thereafter be permanently immune to hog cholera ; but if the event of infection is delayed much longer, it will find the animal susceptible to the disease. In other words, if infection takes HANDLING HOG CHOLERA IN THE FIELD 163 place while passive immunity due to serum alone still exists, a permanent immunity is acquired; if it takes place after the passive immunity dis- appears, the animal will readily contract hog cholera; and, except where hogs are quite closely confined, chance alone must decide whether any particular individual will become permanently im- mune, or, failing in this, eventually die of hog cholera. Method number two will produce more reliable results. The sick are distinguished from the well by physical appearance and temperature read- ings. In handling herds in this manner it is our custom to give serum alone to all animals showing temperatures above 104° F., and to all visibly sick, and not at the point of death, regardless of tem- perature reading. If, however, the weather is warm, and if the hogs are excited in handling, most temperatures will rise above this point, and the thermometer gives us very little information. Under such circumstances physical appearance is our only guide. A useful practice, whenever con- ditions are such that it can be employed, is to feed the hogs a little grain and to place those that leave the feed in a few moments among the sick that are to receive serum alone, and those that remain for a longer time and eat greedily, among the well that are to receive serum and virus. Practically all will eat a little, but the infected animals are 164 HOG CHOLERA first to leave their feed. Any method of distin- guishing the sick from the well is only approxi- mately correct, but a herd handled in the manner we have outlined will emerge from the treatment permanently immune to hog cholera. On the whole, this method of handling is quite satisfac- tory, but it is open to the objection that we may introduce a more virulent strain of virus into herds already infected, and we may be accused of killing animals when we have merely failed to pre- vent their death. This method is practicable only when the owner of the animals fully realizes that some apparently well hogs in infected herds will die following even serum alone administration, and when he is dis- posed to expect like losses following serum-virus treatment. Veterinarians experienced in handling hog cholera dread to use virus in infected herds, but we meet conditions under which it is wise to do so. Method number three is safest, and, as with method number two, the herd emerges with all animals permanently immune to hog cholera. The added expense is the only objection, but in many instances, especially when the animals are above average in value, it is more than justified. There is great satisfaction to the practitioner, as well as to the breeder, in knowing that nothing has been HANDLING HOG CHOLERA IN THE FIELD 165 done to add fuel to the flames, and in being al- lowed three weeks' respite in which to observe the progress of an outbreak. Irrespective of the plan we choose, if new cases continue to appear later than the sixth or seventh day following treatment, a second dose of serum alone is indicated; and if " breaks" occur subse- quent to simultaneous treatment, they should be handled in the manner described in the preceding chapter. Under the conditions in which we found this herd of shoats, we explain the situation to the breeder, and recommend method number three as safest, informing him at the same time that method number two is, in the majority of cases, satisfactory. With the facts before him he can then decide for himself. Precautions to prevent spread of hog cholera to neighboring farms include preventing sale or ex- change of sick or well animals from the infected herd, exclusion from the infected pasture of all persons, vehicles, or animals that may later enter non-infected hog quarters, and prompt disposal of carcasses so that they will not attract carrion- eating animals or birds. Burning is by far the best method of destroying carcasses, but burying in quicklime, or rendering, is permissible. In a pasture such as we find this herd of shoats dis- 166 HOG CHOLEBA infectants are of little service, and we must de- pend on natural influences (drying and sunlight) to destroy virus which contaminates the soil. Many states have specific regulations governing precautions against interherd spread of hog chol- era, and when these are available and practicable they should be followed. None of the shoats should be removed earlier than thirty days follow- ing disappearance of all sickness from the herd, and previous to their removal, if they are to min- gle with cholera susceptible hogs they should first be dipped or sprayed with 3 per cent compound cresol solution. It is legal in some states, in han- dling a herd of this kind, to remove apparently well animals for immediate slaughter under in- spection, but except in unusual circumstances the practice has little to recommend it. If we go back to our original problem and as- sume alterations in the conditions there outlined, corresponding changes in the plan of handling will suggest themselves, and the reasons for these changes will appear. If hogs are closely confined and the herd is badly infected, serum alone is indi- cated, because natural infection will take place and produce permanent immunity in all that sur- vive ; if they are found under conditions that sug- gest low resistance, if they are of exceptional value, or if the owner is skeptical, nervous, or overcritical, plan number three should be recom- HANDLING HOG CHOLEEA IN THE FIELD 167 mended, special care being taken to build up the resistance of the animals during the interval be- tween serum alone and serum-virus administra- tion. If, as is sometimes the case, we are compelled to make a provisional diagnosis of "hog cholera, we should give serum alone and observe the future development of the disease. Provided it proves to be hog cholera, or if it disappears entirely so that doubt still remains, we may give simultaneous treatment three or four weeks later; if it proves to be some other malady, and if hog cholera is not in the vicinity, simultaneous treatment should not follow unless the owner wishes to maintain an im- mune herd. Usually, when there is hog cholera together with some active complication, the im- munity of the herd should be maintained on serum alone until the animals are in fit condition to re- ceive serum-virus treatment. This may require two or more doses of serum at three or four week intervals, but if the complication is of such nature that it cannot be controlled after serum alone is administered, we will only aggravate it if we give simultaneous treatment. Methods of preventing spread of hog cholera to neighboring herds are also somewhat different when we find the infected animals closely confined. We gain very little by cleaning and disinfecting quarters occupied by hogs sick with cholera, be- 168 HOG CHOLERA cause each time an infected animal urinates, rein- fection of its pen takes place. As long as hog cholera is active in a herd we should devote our attention to effective quarantine, prompt disposal of carcasses, and the maintenance of ordinary cleanliness that is at all times conducive to the health of the animals. When the disease disap- pears, all contaminated litter should be burned, and the indoor quarters sprayed with 3 per cent lysol or compound cresol solution. Often appli- cation of disinfectant at intervals of several days is advantageous. Hog cholera virus cannot al- ways be killed in outside yards. Spreading a thick layer of straw over the yard and burning it is probably most effective, but this is not always practicable. Plowing and free use of disinfec- tants hasten destruction of the virus, but the lat- ter measure is useful only in small enclosures. Too often directions given for disinfecting quar- ters require more than is possible, and they are not specific. If we are careful not to require unneces- sary and laborious measures we will secure much better cooperation in carrying out those that actu- ally are essential; and if surroundings are such that we find it impossible to give detailed and spe- cific directions for cleaning and disinfecting, we may be sure that the general admonition to " clean and disinfect " will do very little good. We must recognize the fact that some hog quarters cannot HANDLING HOG CHOLERA IN THE FIELD 169 at once be freed of hog cholera virus, at least by methods within reach of the man of average means. Under such circumstances, if hog raising is to be continued, the herd should be maintained immune to hog cholera. We have already said that handling a herd of infected shoats is the veterinarian's simplest duty in dealing with hog cholera. We will now con- sider some of the more complex problems that field work constantly place before us. Let us suppose that in addition to the herd of infected shoats there is on the same farm, some distance away, a number of feeding hogs that have shown no signs of disease. If the animals are to be marketed in less than four weeks they may receive serum alone, and if hog cholera does not appear among them in the course of six or seven days, it is allow- able to kill them under inspection; if marketing must be delayed more than four weeks, simultane- ous treatment is indicated. As far as the effect of treatment itself is concerned, hogs may, if emergency demands it, be killed for food as early as one day following administration of serum alone, but if serum and virus are given, a delay of at least three weeks is desirable. In addition to feeders we encounter on practic- ally every farm a considerable number of breeding stock. A boar, pregnant sows, some just farrow- ing, and others nursing litters make up the repre- 170 HOG CHOLEKA sentative farm herd. A permanent immunity is desired for all of these, and we follow the general plan of giving simultaneous treatment to all ani- mals in condition to receive it, and protecting the others with serum alone pending the time when they may safely receive serum and virus. Assuming that breeding stock of this character is on the farm with the infected shoats, but that after numerous temperatures have been taken there is no evidence of disease, it may be handled as follows : the boar may be given serum and virus at once, or if he is of exceptional value, follow-up treatment; sows in early pregnancy may be han- dled in the same manner, but always after the breeder has been informed that simultaneous treatment will sometimes produce abortion, and that the slight danger must be accepted as a lesser evil ; sows due to farrow in less than three weeks and those that have pigs a few hours or days old cannot safely receive virus. It is true that the infection on the farm will in most cases ultimately reach them, but our aim should be to delay this as long as possible, and to protect the sows with serum alone in the meantime. Continued isola- tion of the sows is desirable. Two or even three doses of serum alone at three or four-week inter- vals may be required before the time is ripe for the final simultaneous treatment, but the extra ex- pense is greatly to be preferred to the alternative HANDLING HOG CHOLEEA IN THE FIELD 171 — that of using simultaneous treatment so that the sow will be farrowing or nursing a newborn lit- ter at a time when the resulting reaction is in progress. The pigs likewise should be maintained on doses of serum alone at four-week intervals until they are at least nine weeks old, preferably twelve, and then they should receive simultaneous treatment. If they are fairly well isolated from the infected animals the first dose of serum alone may be de- layed until they are two or three weeks of age, otherwise it should be given when they are only a few days old.1 aThe question whether young pigs acquire a permanent immu- nity as a result of simultaneous treatment is yet unanswered. Niles describes experiments indicating that they do, while Cahill on the other hand found that over 50 per cent of several hundred pigs given serum and virus between the ages of two and eight weeks failed to acquire a permanent immunity as a result. Peter- sen found that only fifteen out of one thousand ' ' baby pigs ' ' given simultaneous treatment proved susceptible as old hogs. We have collected very little experimental data on this point, the results agreeing substantially with those of Niles. Our field observations, however, lead us to believe that a per- manent immunity is not always established when serum and virus are given to sucking pigs. In one instance we gave simultaneous treatment to fifty pigs that were about eight weeks old. When the animals had reached a weight of about 150 pounds, one of them was brought to us for autopsy and showed undoubted lesions of hog cholera. Three or four of the others developed symptoms of the disease during the following week, so the entire herd was revaccinated. Two of those that sickened died later but we did not have an opportunity to perform autopsies. There is little doubt that they died of hog cholera, but just how many more would have died in the absence of a second injection is a matter of conjecture. In another instance that came under our observa- tion about eighty young pigs were given simultaneous treatment, and when these animals reached a weight of about 180 pounds each, approximately twenty of them died. We performed autop- sies on several, and found unmistakable hog cholera lesions. 172 HOG CHOLERA We have been called on repeatedly to handle herds of sows infected with hog cholera just at farrowing time. Whenever it is possible we dip the animals, segregate them as best we can and administer serum alone, carrying both sows and pigs along with doses of serum alone at four- week intervals until the latter are weaned and at least nine weeks old, at which time sows and pigs receive simultaneous treatment. In herds in which isolation is impossible, we follow the same course in regard to administering serum, giving the first dose, about 4 mils, when the pigs are a day or two old. It is possible to bring pigs safely These observations do not carry the weight that may be attached to carefully controlled experiments, but they suggest caution in regard to the sweeping conclusion that all young pigs acquire permanent immunity as a result of simultaneous treatment. Closely bound up with this question is the one of the immunity of sucking pigs to hog cholera. Pickens found that 100 per cent of pigs nursed by immune mothers were themselves immune, but any person with extensive experience in handling hog cholera knows that we cannot always, or usually, depend on this immunity. We have repeatedly seen pigs born of immune mothers and nursed by them dead with hog cholera before they were four weeks old, but there are others, as Pickens' experiments show, that are immune. Collectively, all experimental work and clinical observations so far recorded point to the conclusion that some pigs of cholera immune mothers are themselves immune, and others are not; some will acquire active immunity as a result of simultaneous treat- ment, others will not. We have no way of knowing whether any particular young pig or litter will acquire permanent immunity if simultaneous treatment is given, so we prefer to maintain the immunity of all young pigs with serum alone, and to finish with simultaneous treatment when the animals are about twelve weeks old. A cheaper plan than this will be available in well-kept herds f the findings of Niles are confirmed; a more effective one is not likely to be found as long as we use serum and virus as they are now prepared.. HANDLING HOG CHOLEKA IN THE FIELD 173 through an outbreak even when they are born in pens containing hogs sick with cholera, and this presents no great difficulties when the sows are immune, but when farrowing and recently far- rowed sows are susceptible, they do not tolerate virus well. Despite the fact that they receive serum a few will die, other will fail to nurse their litters, and on the whole results are much less satisfactory than they are when reasonably effec- tive isolation can be practiced. We do not wish to convey the impression that after hog cholera reaches a herd we can prevent, by isolation, ultimate infection of all the animals in it for exactly the reverse is true. The point we emphasize is that when the disease appears among sows that are farrowing, infection of many of them can be delayed by isolation, that they gain valuable time, and they and their litters are in better condition to withstand the effects of the virus when later it reaches them, either by natural means or through simultaneous treatment. A sow undergoing serum-virus reaction when her litter is a day or two old is in some danger of death, and even if she lives lactation may cease and her pigs perish. Delay the event of infection four weeks, and regardless of how it affects the sow the litter can be saved. The theoretical grounds for handling farrowing sows in this man- ner are obvious, but we recommend the plaij of 174 HOG CHOLEEA isolation only because repeated trials have proved it effective. Establishing and maintaining a hog cholera immune herd. So far we have dealt with hog cholera after it has reached the herd. We are now to consider methods of preventing it from in- fecting the herd, which yield even better results. In their relation to the prevention of hog cholera, most herds fall into three general classes: those from which the virus can be excluded ; those con- stantly threatened with hog cholera; and pure- bred herds from which immune breeding stock is sold. The herds in the first class do not require immunization; those in the other two classes are best maintained immune. The first question to be decided when a client consults his veterinarian is whether it is really necessary for the herd to be maintained immune. Is hog cholera prevalent in the vicinity? Has it appeared periodically on the farm in question? Is the herd subsisting partially or wholly on gar- bage f Is the breeder buying in hogs at frequent intervals? Does he take sows to neighboring farms to be bred, or are sows brought to his farm for the same purpose? Has he an established market for immune breeding stock, or does he wish to establish one? Has the herd access to a stream that may be contaminated with hog chol- era virus ? If all these questions can be answered HANDLING HOG CHOLERA IN THE FIELD 175 in the negative we should advise the breeder not to immunize. It is an unnecessary expense, and when once simultaneous treatment is employed in a herd there is some danger in discontinuing its use. Pigs thus immunized may eliminate vir- us, and this may be on hand to infect susceptible animals that subsequently are added to the herd by birth or purchase. In case it is desired to dis- continue immunization, at least four months, and preferably six, should elapse between the date when simultaneous treatment is last used on the place, and that of the introduction of susceptible recruits into the herd. All of these facts should be perfectly clear to the breeder before virus is used in his herd. When chances of infection with hog cholera are remote, and the breeder is advised against main- taining an immune herd, he should be cautioned against all the practices that may result in the in- fection of his swine. He should also be informed regarding the things that would lead him to sus- pect the presence of hog cholera, and the neces- sity for early reporting of an outbreak, should it occur, must be made plain. When hog cholera threatens ultimately to attack a herd and destroy it we can render the breeder no greater service than in advising him to main- tain it immune to cholera. Much as we dislike the idea, in the abstract, of introducing virus into 176 HOG CHOLEEA new territory, our experience in concrete cases is that one untreated cholera infected herd in a neighborhood is more of a menace to adjacent herds than ten properly maintained immune with simultaneous treatment. In the untreated, in- fected herd, there is a great temptation sometimes to sell animals before a diagnosis of cholera is made, some breeders are slow to accept the fact that hog cholera is in their herds, and on the whole the attack comes on unheralded, and much damage is done before its true nature is realized. On the other hand, when we administer simultane- ous treatment to a herd we deliberately establish our defenses against the spread of hog cholera that may possibly result from it, the period of acute danger is quickly passed, and the herd is no longer a menace to others in the vicinity. When once the breeder decides to maintain his herd immune to cholera, the practice must be faith- fully carried out. Between keeping all animals immune to cholera at all times and declining to use any virus whatever, there is no middle ground. We cannot temporize with a disease like hog chol- era. Like the proverbial nettle, simultaneous treatment incident to maintaining a cholera-im- mune herd must be grasped firmly or avoided alto- gether, for it will not do to have virus and suscep- tible pigs in the herd at alternate intervals. Sooner or later the two will get together. HANDLING HOG CHOLERA IN THE FIELD 177 Let us suppose that a breeder of pure-bred hogs wishes to establish a trade for immune breeding animals, and has decided to maintain a cholera im- mune herd. His herd consists of two large herd boars, fifty brood sows nursing litters about four weeks old, fifty gilts recently bred and now being sold daily in twos and threes as the trade de- mands, and a herd of one hundred fattening hogs that will be ready for market in six weeks. Hog cholera is not threatening the herd. How is" it to be handled with the greatest safety, and with the least expense and inconvenience? The brood sows are not in the best condition to receive simultaneous treatment, the gilts could not be sold and shipped at once if it were given, and the fattening hogs will be sold anyhow in six weeks. If we wait that length of time the gilts also will be sold, the young litters will be weaned, and sows and pigs will be in condition to receive simultaneous treatment. The two boars are thus the only animals in the herd for which the delay of six weeks is not positively indicated, and they can be immunized as well at one time as another. From this concrete example we develop the sim- ple rule that when choice is allowed we begin im- munizing at a time when the herd is at a minimum as far as numbers of adult breeding stock is con- cerned, and when the animals are in condition to receive simultaneous treatment with the least pos- 178 HOG CHOLEEA sible risk. In the average farm herd the most opportune time to immunize is three or four weeks after the spring litters are weaned. On the other hand, when the herd is immediately threatened with hog cholera we have no choice but to accept it as it is, and protect it at once. Under such circumstances the plan is to give simultane- ous treatment to all animals in condition to re- ceive it, and serum alone to the remainder. Every four weeks we return and repeat the process, con- fining the treatment to those that received serum alone previously, until the entire herd has received simultaneous treatment, and permanent immunity has thus been established. When once the adult breeding stock is immune, our task is then to immunize the young litters as they come on. This is relatively simple for the veterinarian and inexpensive for the breeder. On farms where methods of swine husbandry are the best, and at times when there appears to be little immediate danger from hog cholera, the best plan is to keep close watch on the pigs until they are about twelve weeks old and then give simul- taneous treatment. In many herds though, es- pecially the large garbage-fed herds in the East, a high percentage of the pigs will, if left unpro- tected, contract hog cholera before they reach an age approaching twelve weeks, and a considerable number that do not actually contract the disease HANDLING HOG CHOLERA IN THE FIELD 179 will fail to develop so as to be fit subjects for simultaneous treatment. In these herds, the only effective plan we know of is to protect the pigs with serum alone until they are old enough and in proper condition to receive serum and virus. Un- der ordinary conditions the pigs receive serum alone when they are between three and six weeks of age, they are weaned when they are about eight weeks old and receive simultaneous treat- ment two to four weeks later. It is best to cas- trate them as sucklings. Under exceptional con- ditions we are compelled to give more than one dose of serum alone before the time is ripe for simultaneous treatment, but an extra dose of se- rum for a small pig is not expensive. We have used this general plan since 1912, starting with several garbage-fed and cholera in- fected herds in quarters that did not permit clean- ing and disinfecting, and protecting all subsequent litters of pigs, year after year, with losses from all causes totaling considerably less than five per cent. We know of several other veterinarians who have obtained like results during a term of years, and we do not know of a single instance where the plan has been followed consistently and found wanting. The preliminary doses of serum alone are not necessary in all herds, but we may resort to them confidently under conditions such as we have described. 180 HOG CHOLEKA Several points that contribute to the success of maintaining an immune herd remain to be men- tioned. Especially in large herds it is a good practice to mark each pig at the time it is immun- ized so that it can be positively identified. Other- wise we are likely to miss an occasional pig or lit- ter, and if these untreated animals subsequently contract hog cholera, we are called to account for deaths for which we are in no way responsible. We should also suggest to the breeder the advan- tage of breeding several sows near the same time, so that a considerable number of pigs can be im- munized at one time. In addition to economy in immunizing this practice enables the breeder to provide foster mothers for pigs farrowed by sows which on account of death or disease incident to parturition are unable to nurse their litters. It is important that pigs shall grow steadily and rapidly from birth until the time when simultane- ous treatment is administered. Influences that re- tard growth usually lower resistance as well and we are thus compelled to maintain the immunity of poorly nourished pigs with serum alone much longer than is necessary in handling thrifty pigs. Any suggestions that will aid the breeder to grow pigs rapidly during the first three months of their lives will be greatly to his advantage. Handling feeding hogs. A common practice on farms in many parts of the country, more par- HANDLING HOG CHOLERA IN THE FIELD 181 ticularly in the corn-belt, is that of purchasing feeding shoats in the fall of the year to consume the season 's crop of grain. The general tendency is for these shoats to be raised in regions where land is rather cheap, and fattened in localities where higher-priced land compels a more inten- sive type of farming. Direct communication be- tween the breeders who raise the shoats and the feeders who finish them is not generally main- tained. The breeder seeks a seller's market in cities where there are large stockyards, and the feeder habitually goes to these places to buy. Be- fore the discovery of anti-hog-cholera serum, long years of bitter experience had taught feeders that hogs which pass through large public stockyards very often contract cholera. As soon as the serum was discovered it was eagerly seized on in at- tempts to protect stockyard shoats that subse- quently were to be shipped to other farms to be fattened. The desire was to give these animals permanent immunity to hog cholera, so it grew to be a general practice to administer simultaneous treatment to them in the yards, and ship them in the course of a few days to the feeder's farm. Years of experience prove that this practice, though perhaps an improvement over old meth- ods, is frequently the cause of heavy losses, both in the immediate animals treated and in hogs 182 HOG CHOLERA with which they come in contact after they reach their various destinations. Those who follow the practice are merely lucky if they do not sustain heavy losses because they continually ignore the fact that a reaction nor- mally follows simultaneous treatment, and that shipping lowers the resistance of hogs to such an extent that the reaction may prove fatal. When we add to the effects of shipping and simul- taneous treatment those incident to a brief or prolonged .stay in infected yards before the treat- ment is administered, as well as those that grow out of injudicious feeding and watering when the animals reach the end of a journey, fatigued, hun- gry, and thirsty, we have a chain of devitalizing influences that often cause disaster. It is well known also that many swine unloaded at stockyards do not leave home free from dis- ease. Oftentimes a consignment of hogs repre- sents a breeder's final determination to "cash in" on a herd that is badly infested with parasites, that is suffering with some obscure respiratory disease, or one that has recently contracted hog cholera. Despite the fact that apparently well animals are selected from such herds for shipping each animal selected is potentially the source of future trouble. What is one to expect if in pur- chasing hogs for the feed-yard he chances to in- clude even a few individuals of this kind? The HANDLING HOG CHOLEEA IN THE FIELD 183 mere fact that many lots of shoats are shipped long distances to stockyards and after receiving simultaneous treatment are at once reconsigned to distant localities which they reach without im- mediate or subsequent mishap has little bearing on the problem as a whole. It is the fact that many lots of hogs will not endure such handling, and that we cannot always distinguish in advance between those that will and those that will not, that still troubles us. This aspect of the subject will receive further attention in the chapter on "The Control and Eradication of Hog Cholera. " Let us assume that a man living in western New York requires two hundred shoats as feeders. His natural purchaser's market is in the stock- yards at Buffalo, or further west in the hog-rais- ing districts of Ohio. He knows that there are certain dangers connected with shipping hogs and he consults his veterinarian in order to learn how they can be avoided. What precautions should he be advised to take? Other things being equal it is best to purchase direct from the farm, for this avoids unloading animals at large stockyards, and it is much easier to determine the true condition of hogs when we examine them in what may be termed their nor- mal habitat than when we inspect them hurriedly during the excitement and confusion that prevails at the average stockyard. If immune feeders can 184 HOG CHOLERA be purchased from a reliable source on the farm, that is by far the most satisfactory plan. In case that is impossible, our client should be ad- vised to purchase from thrifty farm herds and to assemble the animals on a stated day at a local shipping point. They should then be given serum alone, placed in clean comfortable well-bedded cars, and shipped at once to their destination. When they arrive at the feeder 's farm, they should be placed in dry comfortable quarters and fed sparingly on light foods for a few days. After they become accustomed to the change in feed and quarters — say in two or three weeks — they should be given simultaneous treatment. If circumstances compel our client to purchase at the stockyards, he should if possible see the animals unloaded, and in any event he should not select animals that have been in the yards several days. It is best to avoid mixed lots of hogs, and those that contain a considerable number of dead animals when they arrive at the yards, for these often are shipped to market because of disease. Hogs that cough persistently should not be ac- cepted. When once the selection is made the ani- mals should be given serum alone without delay and shipped at once to their destination. When they arrive at the feeder's yards they require han- dling similar to that accorded animals purchased directly from the farm. HANDLING HOG CHOLERA IN THE FIELD 185 Careful and experienced men can usually select satisfactory feeders in large stockyards, but on the whole there are unavoidable risks associated with the practice. Handling show hogs. Show hogs constitute a separate problem in themselves, because they are of exceptional value, and because they must necessarily be subjected to handling entirely dif- ferent from that accorded the ordinary farm or market hog. It is not uncommon for show hogs to contract cholera during contact with other swine in the show ring or in transit from fair to fair, and not infrequently they arrive home appar- ently well, and develop symptoms of the disease during the few days following, thus infecting the entire herd which they represent. This experi- ence has been so common that the practice of showing hogs that are not immune to cholera is indefensible. Some fair associations require cer- tificates to the effect that hogs are immune to chol- era before they will admit them to the show ring. The breeder who maintains his herd immune to cholera has no difficulties to face from this quar- ter, for as far as hog cholera is concerned, he may send his animals out on the fair circuit secure in the knowledge that they will not themselves be- come infected, nor be instrumental in infecting others with which they come in contact. The breeder whose herd is susceptible to cholera 186 HOG CHOLEKA must have his show hogs simultaneously treated at least thirty days before they leave for the fairs, or else he must give them serum alone at the time they start, and repeat the treatment at three- week intervals as long as they are on the road. Neither plan is entirely free from objection, but either is far from better than to neglect immun- izing. If simultaneous treatment is given this necessitate*, the introduction of virus on a farm where there are untreated susceptible hogs, and thus it is applicable only where there are facili- ties for effective segregation of the show hogs. If serum alone is given and the hogs are infected with cholera at the fairs they must pass through the resulting reaction at a time when they are low in resistance, and if the reaction is so severe that it results in virus excretion, there is danger that in returning from the fair circuit the show hogs may infect the home herd. If simultaneous treatment is to be given show animals and the remainder of the herd is to re- main susceptible to cholera, the following plan is safest: isolate the show hogs in quarters that will permit subsequent disinfection and give them serum and virus; if during the next thirty days none of the animals develop visible sickness, dip or spray them thoroughly, using 3 per cent com- pound cresol solution, and send them out on the show circuit; when they return, it is best to dip HANDLING HOG CHOLEKA IN THE FIELD 187 them a second time before they are placed with susceptible hogs, and where there are facilities for isolating them two weeks after they return this should be done as an additional precaution. We must not lose sight of the fact that even an immune hog can become the intermediate carrier of hog cholera virus. Should a ' ' break " appear when the show hogs are immunized it should be handled according to the plan previously outlined, and as an addi- tional precaution, the entire herd had best be pro- tected with serum. In any event, when the hogs leave the quarters in which they are placed for simultaneous treatment, the pens should be care- fully disinfected. When no virus is to be used in treating the show animals they require serum alone at the time they leave home, and thereafter every three weeks as long as they are on the road. After they re- turn it is well to isolate them two weeks, after which they may be dipped in antiseptic solution and placed with the remainder of the herd. On the whole, a breeder who habitually places hogs in the show ring should maintain his entire herd immune to hog cholera. Under most cir- cumstances, when this is not done the use of serum alone for temporary protection is indicated, but under exceptional conditions, where perfect seg- regation is possible simultaneous treatment may 188 HOG CHOLERA be given the show animals. Not infrequently the practitioner has the question of immunization thrust on him as an eleventh-hour consideration just on the eve of the departure of show hogs for the fairs. In this event he has no legitimate choice but to protect the animals with serum alone during the period of probable exposure. ORDERING SERUM Every veterinarian in country practice is likely sooner or later to be called on to immunize swine against hog cholera, and because much immuniz- ing consists of emergency work, serum must be procured without delay. For this reason the vet- erinarian should establish relations with a reput- able laboratory near at hand so that telegraphic orders from him will be filled promptly. Because they cannot assume responsibility for products that have been in other hands, most laboratories will not allow credit for returned serum and virus and thus it is desirable to order the exact quanti- ties required. Before ordering serum the veterinarian should ascertain the number of hogs to be vaccinated, and their approximate weights. A representative list would appear thus: 1 boar, weight 600 pounds 8 sows, weight 400 pounds each 65 pigs, weight 20 pounds each 50 shoats, weight 60 pounds each HANDLING HOG CHOLERA IN THE FIELD 189 The common tendency is to estimate weights of swine far too low, and this should be thought of in connection with every serum order. Before the list is completed the final question, "Have you any other hogs?" should always be asked, for it is very annoying and very common to find, even after we reach a farm to do the immun- izing, that the owner has hogs which he has not mentioned because he "hadn't thought of having them immunized. " If a simultaneous treatment is to be given to any of the hogs in a herd, the remainder must not go long without some kind of immunization, and lack of sufficient serum to treat an entire herd may often postpone the date of treatment or necessitate a second call. When all of the hogs that are in the herd are listed, the veterinarian can estimate the quantity of serum and virus required, provided he has a dose table from the laboratory he patronizes. Lacking this, he should send in the list and allow the laboratory to make the estimate. Telegrams or letters containing orders such as "Serum and virus for 20 swine " or "Serum to treat a mixed bunch of 100 sows, pigs and shoats ' ' are not sufficient. Every order should state the required quantity of each product, or it should include a list of the number of hogs and their approximate weights. 190 HOG CHOLEEA Most field work falls within the scope of the con- crete instances outlined in this chapter, but it is necessary, as we endeavored to make clear in the beginning, for one who handles hog cholera to understand hog cholera. Our aim throughout has been to show why as well as what, but if we have fallen short of this aim we can at least assure our readers that the methods recommended are con- servative and effective, and that they have been developed as a result of years of field and labora- tory experience. One final thought. The beginner in hog cholera work sooner or later finds himself face to face with some baffling situation. A herd seems in need of immediate protection but doubt in regard to diagnosis, doubt as to whether the complete history of the herd has been frankly laid before him, and the question whether complete coopera- tion will be accorded him in the subsequent han- dling of the herd, render selection of the method of immunizing difficult to make. "When in doubt and emergency requires immediate protection of a herd, use serum alone; then follow with simulta- neous treatment in less than four weeks if subse- quent development of the disease requires it" is the final caution we leave with the beginner. DANDLING HOG CHOLEKA IN THE FIELD 191 The Veterinarian's Charge for Serum and Its Administration If a veterinarian expects to remain long in prac- tice he must render service worth much more than the charge he attaches to it, and the benefit derived from his calls must be obvious to his clients. The fact that immunization of hogs, especially large herds in localities where hog cholera is prevalent, results in a great and obvious saving to the breeder has placed this phase of veterinary prac- tice almost in a class by itself. We do not ac- tually render a greater service in checking an out- break of hog cholera than we do in eradicating tuberculosis from a cattle breeder's herd, but hog cholera is an acute and fatal disease and the direct saving due to its control is far more appar- ent to the breeder than some other services, equally as valuable, that we render him. Because of this fact, and because of the great demand that has existed for the services for veterinarians in immunizing swine, certain abuses in regard to charges for serum administration have come to light. Complaints have been leveled at a few shortsighted and greedy individuals, but they have reacted to the dicredit of the profession as a whole. Especially when large numbers of hogs are vaccinated in one day, when charge is made by the head, and a profit greater than is fair is added 192 HOG CHOLERA to the serum used, the veterinarian goes home leaving his client believing that he, and other members of the profession, are shameless prof- iteers. The natural inference is that other pro- fessional charges as well are exorbitant, and this, as all veterinary practitioners know, is not true. When immunization of a herd of hogs is really indicated and when a veterinarian does the work thoroughly and conscientiously, he renders a great and obvious service, and is entitled to a fee con- siderably above that which the average breeder is inclined to regard as fair. The breeder would be surprised if he knew the cost of waste, breakage, and overhead which the veterinarian must pay. We believe though, that instead of courageously charging fees which are actually their due, and which will enable them to use first-class products and do careful work, too many veterinarians have yielded to a temptation to collect their fees, un- known to the breeder, in the form of profit on the serum used. The purchase price of the serum sooner or later comes to light and in the absence of previous explanation, the breeder naturally be- lieves that the difference between the price the veterinarian pays and the price he charges his clients for serum is all profit. Real and imagin- ary abuses in this direction have led to actual and proposed legislation designed, on the one hand, to place vaccination of hogs largely in the hands DANDLING HOG CHOLEKA IN THE FIELD 193 of laymen, and on the other hand to fix the margin of profit which the veterinarian may charge, or at least to prevent1 him from concealing from his client the purchase price of the serum he uses. Legislation of the former type can result only in disaster to the swine industry and harm to the veterinary profession, but we do not believe there are good reasons why the purchase price of serum should not be known to the breeder. Obviously the profession puts itself in a bad light when it opposes legislation of this kind, unless it can justly be opposed on the ground that the handling charge proposed is not sufficient to cover costs of waste and breakage. Such opposition only gives sub- stance to the suspicion that there is something to conceal. It is a principle which should be ob- vious to all that if the veterinary profession is to retain exclusive rights to administer serum and virus it must exercise these rights in a manner to justify this exclusion ; and any legislative attempts to discipline the occasional renegade who habitu- ally reaps an excessive profit on serum should, and we believe will be, welcomed by the better ele- ment in the veterinary profession. The veterinarian's fee for his work is his own private concern, and the compensation he can com- mand depends for the most part on the skill and knowledge which he employs to benefit his client ; but the best interests of the public demand that the 194 HOG CHOLEKA use of serum and virus shall be placed exclusively in his hands, and when this is done he has not the same right to fix the selling price of these products that he has to name his own fee. Use of serum and virus is a public trust reposed in him rather than a monopoly given into his hands for private exploitation. His profits should come from his work, not from the serum he uses. Some practitioners charge according to the num- ber of hogs treated, some according to the quantity of serum injected, and others on the basis that they fix fees for other calls. vNo system is entirely free from objection, but we believe that the most satisfactory and fair plan is for the veterinarian to place a value on his day's work and charge for vaccinating according to the time consumed in doing it. He is entitled to add to this a handling charge on the serum he uses, to compensate for clerical work, express, breakage, and unused prod- ucts that are left on his hands. Under ordinary conditions, if breeders pay cash, an increase of 20 or 25 per cent over the purchase price will take care of these items, but it will not be sufficient if credit is habitually allowed. A practitioner can lose more on one bad serum bill than he can collect as fees for several days' work. The practice of charging according to the time consumed has obvious advantages if we let our clients know that we are following it. It con- HANDLING HOG CHOLEftA IN THE FIELD 195 sumes less time to vaccinate a given number of hogs for a client who will have the animals se- curely penned in clean dry quarters, and plenty of help ready for work when the veterinarian ar- rives, than it does to vaccinate one-fourth that number for a man who awaits the veterinarian's arrival and then begins a frantic or leisurely search for gates, lumber, ropes, and other needed paraphernalia. A veterinarian cannot consume several hours in vaccinating a small lot of pigs and at the same time keep his fee at a figure that the breeder can afford to pay. The breeder who provides facilities and help so that the work may be done dexterously and rapidly should profit by his foresight; the one who is neglectful must ex- pect to pay for his negligence. Emergency hog cholera practice, that is, the care of herds already infected, will come regularly to a man who handles it with only a fair degree of effectiveness. Under such circumstances even average veterinary service is far better than none. The same rule does not apply in maintaining im- mune herds, the phase of hog cholera control that offers greatest satisfaction to both practitioner and breeder. If the breeding in a herd is so or- dered that a large number of pigs can be vaccin- ated at one time, if the animals are grown rapidly and conditioned so that they will withstand simul- taneous treatment at an early age, and if the 196 HOG CHOLERA breeder habitually provides facilities that allow vaccinating to be done without loss of time, the cost per head can be kept at a minimum. The veterinarian who so advises his clients as to bring these things about is the only one who can hope to enlarge m's swine practice and gain lasting success in hog cholera work. A system of wireless which we do not completely understand, but which nevertheless spreads intelligence rapidly and un- erringly in country districts, will, in each veterin- arian's community ultimately convey the news that immunizing pays, or that it does not pay ; and the veterinarian must have it whispered abroad that immunizing their herds pays his clients or he will "kill the goose that lays the golden egg." CHAPTER X HOG CHOLERA, MEAT INSPECTION AND GARBAGE FEEDING HOG cholera is a widespread disease affecting just one species of animal used solely to produce meat for human food, and its status as far as meat inspection is concerned is necessarily well estab- lished. The following paragraphs from Edel- mann1 set forth the broader principles which gov- ern the formulation of more detailed and specific regulations which are in force in various abattoirs throughout the country : "Judgment of the meat in swine erysipelas swine plague and hog cholera. In view of the fact that meat of these diseased animals has frequently been eaten for food without ever having incurred any impairment or injury to man, it can hardly be classed as injurious to health. In individual cases however the following should be considered: "1. The entire carcass is unfit for food as soon as marked substantial changes (congestion of blood, serous infiltration, degeneration, yellow discoloration) of the musculature or fatty tissue are observed or when marked emaciation has occurred. 1 Udelman, Meat Hygiene (English translation by Mohler and Eichhorn; 2d edition, 1911). 197 198 HOG CHOLEKA 11 2. In all other cases, with the exception of the chronic forms of swine plague and the sequelae of this disease and those of hog cholera, the carcass in all of these diseases is to be considered fit for food but subject to certain conditions. For veterinary sanitary reasons, and partly in consideration of the causative agents in the blood of swine erysipelas, swine plague and the acute forms of hog cholera, the meat and fat are to be boiled, steamed (rendered into lard) or pickled. The portions affected by the disease should be condemned. 11 3. In case of slow chronic forms of swine plague without disturbance of the general condition, or sequelae of this disease (adhesions, cicatrices, capsulated caseated areas etc.) or of hog cholera (caseation of mesenteric lymph glands, adhesions of intestines, formation of cica- trices in the intestinal mucosa) only the affected portions of the meat are to be condemned and destroyed. The remainder of the carcass is fit for feed without any re- striction. ' ' It will be observed that swine plague and swine erysipelas are governed by the same general con- siderations that apply to hog cholera. In view of the fact that swine plague occurs most frequently as a complication of hog cholera as well as of the fact that rapid differentiation of all three dis- eases based on abattoir examinations alone is not possible, it is fortunate indeed that these diseases run so nearly parallel in their relation to meat inspection. From the excerpt from Edelmann we glean the following essential considerations: first, the fit- ness of the meat for human food is based on patho- HOG CHOLERA AND MEAT INSPECTION 199 logical changes in the meat itself, and is not deter- mined by the probable presence or absence of the causative agents of hog cholera, swine plague or swine erysipelas ; second, carcasses of hogs which before slaughter were obviously suffering with any one of the three diseases, may, in the absence of extensive pathological changes in the meat it- self be passed for human food, but for veterin- ary sanitary reasons it should be boiled, rendered or pickled in order to destroy causative agents of either of the three animal diseases which it may contain. A review of these facts leads logically to the conclusion that as far as hog cholera is concerned there is, and can be, no sharp line of demarcation between carcasses that are fit for human food and those which are unfit, because it has not been shown that hog cholera virus is injurious to man. The more important phase of meat inspection as it applies to hog cholera centers around the de- cision which determines whether a particular car- cass requires special treatment (boiling, render- ing or pickling), in order that parts of it may not subsequently infect other swine. Edelmann states clearly the need for a distinction between the fit and the unfit based solely on veterinary sanitary reasons, but he is silent as to how this distinc- tion is to be made. The U. S. Bureau of Animal Industry meat in- 200 HOG CHOLERA spection regulations are much more specific in regard to the manner in which the distinction be- tween the fit and the unfit shall be drawn, but the distinction is based wholly on considerations deal- ing with the fitness of the meat for human food. Veterinary sanitary considerations, which would include atempts to require cooking or rendering of all carcasses which contain hog cholera virus, do not enter in. The parts of these regulations which refer specifically to hog cholera read as fol- lows: " Regulation 9, section 2, paragraph 2. All hogs plainly showing on ante-mortem inspection that they are affected with either hog cholera or swine plague shall be marked 'U. S. condemned' and disposed of in accordance with section 8 of this regulation. "Regulation 9, section 2, paragraph 3. If a hog has a temperature of 106° F. or higher, and if it is of a lot in which there are symptoms of either hog cholera or swine plague, in case of doubt as to the cause of the high temperature, after being marked for identification, it may be held for a reasonable time, under supervision of an inspector, for further observation and taking of temperature. Any hog so held shall be reinspected on the day it is slaughtered. If upon such reinspection, or, when not held for further observation and taking of temperature, then on the original inspection, the hog has a temperature of 106° F. or higher, it shall be condemned and disposed of in accordance with section 8 of this regulation. "Regulation 9, section 2, paragraph 6. All animals which, on ante-mortem inspection, do not plainly show, but are suspected of being affected with, any disease or HOG CHOLERA AND MEAT INSPECTION 201 condition that, under these regulations, may cause con- demnation, in whole or in part, on post-mortem inspec- tion, shall be so marked as to retain their identity as suspects until final post-mortem inspection, when the car- casses shall be marked and disposed of as provided else- where in these regulations, or until disposed of in ac- cordance with section 7 of this regulation. ' Regulation 9, section 4, paragraph 1. All hogs, even though not themselves marked as suspects, which are of lots one or more of which have been condemned or marked as suspects under section 2 of this regulation for either hog cholera or swine plague, shall so far as possible be slaughtered separately and apart from all other animals passed on ante-mortem inspection. "Regulation 9, section 7, paragraph 3. A hog sus- pected of being affected with hog cholera or swine plague may be set apart and held, under bureau supervision, for treatment with anti-hog-cholera serum. If at the expiration of the treatment period the animal upon examination is found to be free from disease it may be released for any purpose. "Regulation 9, section 8. Except as hereinafter pro- vided in this section, animals marked 'U. S. condemned' shall be killed by the establishment, if not already dead, and shall not be taken into an establishment to be slaughtered or dressed; nor shall they be conveyed into any department of the establishment used for edible products; but they shall be disposed of and tanked in the manner provided for condemned carcasses in regula- tion 14. The 'U. S. condemned' tag shall not be re- moved from, but shall remain on, the animal when it goes into the tank. The number of such tag shall be reported to the inspector in charge by the bureau em- ployee who affixed it, and also by the bureau employee who supervises the tanking of the animal, provided, that any animal condemned on account of hog cholera and swine plague, as prescribed in paragraph 1, 2, 202 HOG CHOLEKA or 3 of section 2 of this regulation, may be set apart and held, under bureau supervision, for treatment with anti-hog-cholera serum, the requirement that such ani- mal shall be killed shall be held in abeyance to await the result of the treatment. If at the expiration of the treatment period the animal upon examination is found to be free from disease, the 'U. S. Condemned' tag shall be removed and the animal released for any purpose. " Post-mortem inspection. "Regulation 11, section 4, paragraph 1. The car- casses of all hogs marked as suspects on ante-mortem inspection shall be given careful post-mortem inspection ; and if it appears that they are affected with either acute hog cholera or swine plague they shall be disposed of in accordance with paragraph 2 of this section. "Regulation 11, section 4, paragraph 2. Carcasses of hogs that show acute and characteristic lesions of either hog cholera or swine plague in any organ or tissue, other than the kidneys or lymph glands, shall be condemned. Inasmuch as lesions resembling those of hog cholera or swine plague occur in the kidneys and lymph glands of hogs not affected with hog cholera or swine plague, carcasses of hogs in the kidneys or lymph glands of which appear any lesions resembling lesions of hog chol- era or swine plague — shall be carefully further in- spected for corroborative lesions. On such further in- spection— "(a) If the carcass shows such lesions in the kid- neys, or in the lymph glands or both, accompanied by characteristic lesions in some other organ or tissue, then all lesions shall be regarded as those of hog cholera or swine plague, and the carcass shall be condemned. "(&) If the carcass shows in any organ or tissue, other than the kidneys or lymph glands, lesions of either HOG CHOLERA AND MEAT INSPECTION 203 hog cholera or swine plague which are slight or limited in extent, it shall be passed for sterilization in accord- ance with regulation 15. " (c) If the carcass shows no identification of either hog cholera or swine plague in any organ or tissue other than the kidney or lymph glands it shall be passed for food unless some other provision of these regulations requires a different disposal." For years it has been a common practice among swine raisers to consign hogs to market as soon as hog cholera appeared among them, and even at the present day, when an effective preventive of the disease is at hand, the custom still prevails. If an entire herd consists of hogs nearing com- pletion of the fattening period, and if cholera is recognized as soon as it appears, the loss to the feeder is not heavy. He promptly markets all hogs that are apparently well, leaving behind the few that are visibly sick. If, though, a herd in- cludes sows, pigs and shoats which cannot be mar- keted to advantage, or if it consists of pure-bred animals, heavy and unnecessary loss must be ac- cepted in consigning it to market. Unfortunately the loss is not confined to the man who ships the infected hogs. His herd becomes a menace to others in the vicinity as it is driven to the nearest loading station, and it helps to perpetuate the in- fection which, existing in practically all large pub- lic stockyards in the country, threatens all cholera susceptible swine not intended for immediate 204 HOG CHOLEKA slaughter. Nor is the danger terminated when the hogs reach the shambles. An impression pre- vails that in establishments where meat inspec- tion regulations are in force, carcasses that con- tain hog cholera virus are condemned, and those that do not contain it are passed for food. This is not the case. Many carcasses that contain the virus readily pass inspection, and although they are perfectly fit for human food, trimmings from them regularly find their way into garbage, and when this is fed to susceptible hogs, they, in turn, contract disease. It is a vicious cycle, and one very difficult to break. When a consignment of hogs from a cholera infected herd reaches an establishment where fed- eral meat inspection regulations are in force it is first subjected to ante-mortem inspection. With respect to hog cholera it may contain five classes of hogs: first, dead hogs; these are condemned and tanked: second, hogs that show undoubted symptoms of cholera; these also are condemned and tanked: third, those that show suspicious symptoms and temperatures below 106° F., these are slaughtered ; carcasses that show hog cholera lesions are condemned or passed for sterilization according to the extent of the lesions; those that show no lesions are passed for food : fourth, hogs apparently normal, and those which show suspi- cious symptoms, having temperatures above 106° HOG CHOLEBA AND MEAT INSPECTION 205 F. ; these are condemned or isolated for further temperature records; in case further tempera- tures are taken the animals are condemned if the readings are still above 106°; otherwise they fall into class three or class five : fifth, apparently nor- mal hogs that show temperatures below 106°; these pass ante-mortem inspection and post-mor- tem as well if they do not show lesions of hog chol- era in organs other than the kidneys or lymph glands. Let us consider the individual hog. Briefly stated, the requirements in order that it may pass inspection are that it shall not show conclusive symptoms of hog cholera, it shall not show sus- picious symptoms plus hog cholera lesions, it shall not maintain repeated temperature readings above 106° F., and regardless of ante-mortem findings the carcass shall not on post-mortem show hog cholera lesions in organs other than the kidneys or lymph glands. What are the chances for car- casses that contain hog cholera virus to pass in- spection ? This question is best answered by considering the average case of hog cholera. Let us suppose that a hog becomes infected to-day. According to Dorset, "Bepeated experiments have shown that the blood of pigs that have previously been in- oculated with the virus of cholera becomes infec- tious for others within twenty-four hours; the 206 HOG CHOLERA urine and f eces contain the virus usually in forty- eight hours, and the secretions of the eyes and nose become infectious by the third day follow- ing infection: therefore these experiments show that infected pigs are capable of transmitting the disease before they themselves show any visi- ble illness." l Thus the blood and therefore the meat of a hog infected to-day will to-morrow contain hog cholera virus sufficient to infect others, but there will be neither symptoms, temperature readings nor le- sions to cause its condemnation. The same will be true on the second, third and fourth days fol- lowing infection, but from that time on we may at any time expect developments that would cause condemnation. These may, though, be delayed several days longer. There is a time, at least three days on an average, in the lives of practi- cally all hogs affected with acute hog cholera when they will pass inspection and when bits of pork from their carcasses will infect other swine to which they are fed. This interval varies from one or two to several days, and is measured, roughly, by the time required, after the first twenty-four hours following infection, for the temperature to rise to 106° F., or for conclusive symptoms or extensive cholera lesions to appear. 1Keport of the chief of the U. S. Bureau of Animal Industry for the year ending June 30, 1917. HOG CHOLERA AND MEAT INSPECTION 207 With these facts in mind, let us again consider the farm herd from which cholera infected hogs are shipped. Often a considerable number must die before the owner will admit, even to himself, that he is dealing with hog cholera. Then there is the delay incident to securing transportation, and there are many hours during which infected and sound animals are crowded together in a stock car. Finally, after the hogs reach the yards there is an additional delay of several hours or even several days before they are killed. Any person familiar with hog cholera knows that in such a consignment a great majority of the hogs become infected before they are killed and any person familiar with present-day meat inspection regula- tions knows that under such circumstances the vast majority of the infected animals will pass in- spection. The hogs have every chance to become infected but the disease does not have time to develop sufficiently to cause their condemnation. The practice of marketing swine herds as soon as cholera appears is no longer necessary. It rarely profits the man who follows it, and it per- petuates hog cholera, working great harm to the swine industry. Before the discovery of protec- tive serum a herd of hogs once infected with chol- era became a total loss unless some of the animals could be salvaged by slaughter. With the plenti- ful supply of serum now available an infected herd 208 HOG CHOLERA can safely and profitably be kept at home. All that is required is prompt reporting, prompt diag- nosis and prompt serum treatment. With few exceptions serum will, at any given time, save all hogs which are not at that time already danger- ous carriers of hog cholera virus. In the United States, during the decade ending in 1911 approximately 18,000 hogs were condemned annually on account of hog cholera. In 1914 the number reached a total of 116,000; in 1917, 33,000. According to Bureau of Animal Industry estimates, 40 per cent of the pork which is killed and 15 per cent of that which is marketed in the United States is slaughtered on farms or in abat- toirs in which no inspection is maintained. Judg- ing from my study of the situation as a whole, my belief — which I would be reluctant to express in concrete terms if it were not essential to convey at least an approximate idea of existing conditions — is that in the country at large, for each hog which is condemned for cholera, at least three virus-con- taining carcasses pass or evade inspection. What becomes of them subsequently? Each infected carcass possesses almost infinite possibilities in regard to its final distribution. Whether the pork reaches the consumer in the form of hams, shoulders, or bacon, or whether it is fresh, refrigerated or cured, we should not lose sight of the fact that it actually contains unlabeled HOG CHOLERA AND MEAT INSPECTION 209 hog cholera virus, and that uncooked portions of it fed to susceptible hogs will produce cholera. Of the various preserving and preparing proc- esses to which pork is subjected before being sent to the consumer, only one that we know of — cooking — is certain to destroy hog cholera virus which it may contain. According to extensive experiments * which we have carried out the virus lives in fresh meat until decomposition sets in, it is not affected by prolonged refrigeration, and a representative sugar curing and smoking process killed it in only 43 per cent of the tests made. So far we have dealt chiefly with the facts sur- rounding hog cholera and meat inspection as they have been determined by exact scientific methods and recorded data. It remains to be added that clinical observations are entirely in accord with these facts. We hear of one outbreak of hog chol- era in Canada, and it is traced to a consignment of infected hams ; we hear of another in a remote lumber camp in the Adirondacks where hogs are kept to consume the kitchen refuse; and of still another on an inaccessible farm in Nevada follow- ing purchases of market pork. These are merely representative instances. At least 90 per cent of the outbreaks we encounter in New York can be traced to no other source than infected pork trim- 1 Report of New York State Veterinary College 1915-1916, page 60. 210 HOG CHOLERA mings in garbage, and in other Eastern states the situation is essentially the same. Torrance l reports similar conditions in Canada. In the Southern and central states a much smaller pro- portion of herds become infected through the agency of pork trimmings from carcasses that contain hog cholera virus, but even in these sec- tions there is ample evidence that the first infec- tion in many outbreaks takes origin in this man- ner. Once established in territory that supports a dense swine population, the .disease spreads rapidly through many other agencies. Meat inspections in field outbreaks of hog cholera. The practicing veterinarian who is called to handle a farm herd infected with hog cholera very frequently is questioned regarding killing and marketing all animals that remain ap- parently well. How is he to advise his clients'? Disregarding, for the moment, legal and sani- tary considerations, and thinking only of the plan that will cause our clients the least immediate financial loss, we will find relatively few instances where immediate slaughter can be advised. These occur principally in herds of feeders about ready for market anyhow, and in herds in which the disease has progressed so far that protective serum offers very little hope. In either case the 1 ' * Garbage Feeding in Eolation to the Control of Hog Cholera, ' J Journal of the American Veterinary Medical Association, Octo- ber, 1921, p. 22. HOG CHOLEEA AND MEAT INSPECTION 211 hogs are worth more as pork than they will ever again be worth on foot, but here legal and sanitary considerations enter in, and it is only where the state law provides for slaughter under inspection and where provision can be made to minimize the danger to other herds that may result from mar- keting the pork, that slaughtering is to be ad- vised. New York, for instance, has a law which permits killing under inspection from herds infected with cholera, but it is only at institutions and on farms where the pork will not be placed on the open mar- ket that we have advised such a course. We hab- itually follow the plan of explaining the situation to our client, and informing him that he has a legal right to kill, but that he has at the same time a moral obligation to protect his neighbor. When we offer at the same time the alternative of serum treatment, giving a prognosis as nearly exact as is possible, there are few who will not decide to use serum or who will not profit by doing so. Indeed in just one instance that we recollect has one of our clients elected to take shelter under the law and disregard his neighbor. This man had a herd consisting originally of about four hundred hogs. Cholera appeared, but he refused to accept our diagnosis. Finally when his herd had dwindled to about one hundred and fifty animals, he decided to vaccinate. It was a forlorn hope, but we began 212 HOG CHOLERA taking temperatures, intending to administer se- rum only to those that showed readings below 104° F. After numerous trials in which we found but a negligible number of readings below 106° F., we gave up the attempt and returned home. Later we were informed from reliable sources that imme- diately on our departure about seventy-five hogs from the herd were shipped to market and that the majority of them passed federal inspection.1 The man in this instance received more for the hogs than he would have received had he administered serum to all of them as an eleventh-hour mea- sure, but he received infinitely less than would have fallen to his lot had he treated the herd with protective serum at the time when he was first warned of the danger. In those instances in which the practicing veter- inarian is called to inspect hogs that are being slaughtered from cholera-infected herds, the fed- eral meat inspection regulations 2 should be se- lected as a convenient guide, but unless it is so specified by state law, they are not to be regarded as inflexible or final. The practitioner must * This must not be construed as a criticism of the administration of the federal meat inspection regulations. It is merely a rather striking example of the fact that the regulations, admirably formulated and enforced to protect human health and human life, cannot be relied on to eliminate from our markets swine carcasses that contain hog cholera virus. a The paragraphs that relate to hog cholera appear near the beginning of this chapter. HOG CHOLEKA AND MEAT INSPECTION 213 adapt his decisions to the conditions under which he is working. If he knows that the pork is to be sold in the open market where it will become the potential cause of future outbreaks, he cannot be justly criticized if he is relatively severe in his decisions ; on the other hand, if the pork is to be retained at the place where it is killed, as it is on some institution farms, for instance, rather ex- tensive hog cholera lesions should be required in order to condemn. Carcasses that are not deemed fit for pork can be partially salvaged in the form of lard. When slaughter on the farm is decided on, ante-mortem inspection should consist first of ob- serving the hogs before they are disturbed, and re- jecting any that obviously are suffering with hog cholera. Then temperatures may be taken of those that remain and any that show readings above 106° F. should be condemned or put aside for subsequent readings. Later if they show tem- peratures below 106° F. they may be slaughtered and post-mortem findings will determine whether the carcass shall be passed or condemned. In case the weather is very warm, or if it is necessary to excite the animals unduly in taking tempera- tures, one may secure more accurate information by giving them a limited quantity of feed and re- jecting those that do not remain at the trough and eat greedily. Nearly all will come to the trough at 214 HOG CHOLEBA first, but those that are suffering most with chol- era will soon return to the nest. Principles governing post-mortem inspection have already been discussed. Briefly, extensive changes in the meat or fat should cause condemna- tion. Hog cholera lesions in the kidneys and lymph glands do not condemn the carcass, al- though in cholera-infected herds such lesions prac- tically always establish its status as a virus car- rier. Carcasses that show hog cholera lesions in the kidneys, lymph glands and other organs as well are not used for pork, but if the lesions are slight in extent the fat may be rendered into lard. Most hogs that appear well on foot pass post-mortem inspection as well. Garbage Feeding Intimately bound up with meat inspection as it applies to hog cholera is the subject of garbage feeding. As we have already shown this prac- tice is the final 'link in the chain which is respon- sible for the introduction of cholera into so many herds of hogs. If meat inspection regulations be- come more stringent, garbage feeding becomes less hazardous; if they become less stringent, or if they are neglected altogether the risks from in- fected pork trimmings in garbage increase. In any event, chance alone decides when any par tic- HOG CHOLERA AND MEAT INSPECTION 215 ular herd that subsists on garbage will contract hog cholera. The larger the herd, the greater the supply of garbage necessary to maintain it, and the more certain it is to become infected. In earlier years feeding garbage to hogs has produced the most surprising and contrasting re- sults. Its feeding value has long been well known, and men who were tempted to utilize it in feeding hogs usually began the practice on a small scale. If hog cholera did not 'happen to reach the herd during the first year, the financial returns were usually gratifying beyond expectations, and the hog raiser enthusiastically increased the size of his herd — at the same time multiplying its chances to become infected with cholera. Thus a common experience was for the breeder to have the savings of one or more years invested entirely in hogs when cholera finally reached his herd and de- stroyed it. Various preventives of the disease incident to garbage feeding were advertised, and magic for- mulas were passed around by word of mouth. Perhaps one man fed salt and sulphur to his hogs and did not lose a single one; another neglected to do this and his entire herd was destroyed. Could any proof be more convincing! But the law of chance was still in operation, and hog chol- era was relentlessly striking down one herd after another, including those which received the lauded 216 HOG CHOLERA preventives with those that did not, in a wholly impartial manner. There was a belief that garbage in itself pro- duced the disease, and there was divided opinion as to whether it was dietetic in nature or whether it was really hog cholera. The trouble was thought by some to be due to a variety of causes — as in truth it was to a limited extent— but when anti-hog-cholera serum was brought into use it was found that this product prevented most rap- idly-fatal infectious disease which had formerly plagued the garbage feeder 's herd. Also the ad- vent of kitchen sinks and drains eliminated soap poisoning due to dish water which was formerly included in garbage. These two advances have placed garbage feeding on a relatively safe basis. The collection and disposal of city garbage is a complex and exacting process, and staggering sums are paid annually for this service. Disposal plants cost huge sums of money as original invest- ments, and coal, labor and upkeep incident to their operation require a heavy and continuous outlay. One city of 100,000 that we know of — and it is no exception — was until recently incurring the ex- pense of collecting its garbage and hauling it three miles to a disposal plant, and it was also operating the plant at an annual expense of $40,000. The garbage was burned and there was no salvage, as HOG CHOLEKA AND MEAT INSPECTION 217 there is in some disposal plants, in the form of grease, tankage and bones. Viewing the subject of garbage feeding from the standpoint of the municipality it may be said that in cities of less than 100,000 feeding is by far the most economical plan of disposal, and ex- perience will probably prove that the same rule holds good for larger cities. If provisions are made for feeding, no city of less than 100,000 should find it necessary to pay disposal costs, and many should be able to offset in some degree, collection costs as well. Cities that elect to dis- pose of their garbage by feeding may maintain piggeries as a municipal function, or they may provide by contract for collection and disposal. We believe the most satisfactory plan is for the city to collect the garbage and deliver it to the contractor's piggery or to a specified loading station. Long term contracts with optional renewals on the part of the contractor are the only ones that will prove satisfactory when the plan is to feed the garbage. No man can afford to build adequate quarters for large numbers of hogs unless there is assurance of a constant supply of feed during a term of years. Short term contracts are respon- sible in large measure for the fact that the gar- bage feeder's establishment is so often a public nuisance. He does not have time to organize his 218 HOG CHOLEEA feeding operations, lie cannot invest in good equip- ment that will have to be sold at a loss as soon as his contract terminates, and there is not sufficient time for the enterprise itself to yield profits that may be returned to it in the form of equipment. When a city wishes to let its garbage contract to the best advantage it should agree to give the contractor all the municipal garbage, and it should provide ordinances that require its drainage and the exclusion of tin cans, broken bottles and the like. Collections should be required at least once a week in winter and twice in summer. A five- year contract which the contractor can renew at his option if he discharges his obligations, is satis- factory, and will serve to entice reliable con- tractors. Municipal piggeries are successful sometimes, but changing city administrations are not always to their best advantage. Sooner or later self- styled "business men" are likely to be charged with their general supervision, and in formulat- ing business rules for their subordinates they themselves are likely to ignore essential natural laws governing swine husbandry and the handling of swine diseases. Business principles must of course be observed, but they must be made to dovetail with principles that conserve the health of the swine and provide each day for their intelli- gent care. HOG CHOLEEA AND MEAT INSPECTION" 219 Garbage varies greatly in feeding value, but as a very general rule one ton of well drained city garbage which is free from extraneous matter will feed about fifty or sixty fattening hogs, causing them to gain from % to one pound each. In other words one ton of garbage should produce about fifty pounds of pork. At least 200 pounds of a good grain ration is required to produce the same gains. Thus as far as the public at large is con- cerned dumped or burned garbage represents a great and avoidable waste, and in states with large urban populations this waste assumes huge proportions. Veterinary Supervision of Garbage-Fed Herds Herds of hogs fed on city garbage are con- stantly threatened with cholera, and for this rea- son they sooner or later come under the veteri- narian's care. The dangers nowadays are fre- quently known in advance and hence professional advice is sought before a herd is assembled, but many feeders are still ignorant of the chances they assume, and still others procrastinate in regard to immunizing. When a veterinarian is consulted before a herd is assembled, or before hog cholera appears in it he can render service of a high order if he is fa- miliar with disease prevention and swine hus- bandry methods. He also assumes considerable 220 HOG CHOLEKA responsibility, for, given a clean herd he is sup- posed to know how to keep it clean. The preven- tion or handling of hog cholera in herds fed on garbage is not different in principle from han- dling the disease in other herds, but there are several difficulties peculiar to the garbage-fed herd that must be overcome. These difficulties are so closely linked up with methods of swine hus- bandry that all must be considered at the same time. Should the garbage feeder raise or purchase feeding hogs ! Many considerations enter in, but as a general rule if the herd is to be relatively small, say less than 500, if there is provision for exercise and a little pasture, if warm farrow- ing pens can be provided, and if a supervisor who thoroughly underctands swine breeding can be se- cured, the ^est plan is to raise the pigs. Under ordinary conditions, as the herd is increased in size, raising the pigs becomes relatively less feas- ible. The question of proximity to a good mar- ket for good feeding shoats likewise must be con- sidered, and what we have said in a preceding chapter in regard to handling feeder hogs, applies here as well. Shoats that have been immunized on the farm are by far the safest purchase, and susceptible ones that can be purchased from thrifty farm herds may be immunized without much danger. Purchase of stockyard hogs is ad- HOG CHOLERA AND MEAT INSPECTION 221 visable at times, but judicious selection and care- ful handling are essential, and even then the best professional care does not always insure against considerable loss from hog cholera and its com- plications. When it is desirable to purchase feeding shoats to consume garbage, those weighing between 75 and 120 pounds are most desirable. Although it is feasible to raise the very best pigs on garbage alone, the fact remains that often they begin to eat it well and put on rapid gains only after they have attained considerable size. It is likewise true that shoats cannot be put on full feed as rap- idly when garbage is fed as they can when their ration consists, of grain, hence it is well to pur- chase rather light shoats so that the loss of time in getting them started can be made up by a rela- tively long fattening period. Except when cholera immune shoats are pur- chased from the farm it is necessary that immu- nizing shall take place before or immediately after they reach the feeder 's yards, and thus they must often undergo the resulting reaction before the condition known in the fattening pen as "full feed" is reached. Special care is necessary not to overfeed at this time. Efforts to crowd the animals beyond their capacity may aid in caus- ing "serum breaks, " and do injury that will re- quire weeks to overcome. , With this one special 222 HOG CHOLEEA precaution our readers are referred to the head- ing in the last chapter entitled ' ' Handling Feeder Hogs." It is in raising pigs entirely on garbage that the greatest care is required. Numerous pitfalls are in the path of the beginner, and it is a quite general rule that one serious disaster is necessary to impress him with the necessity for avoiding neglect. The critical period in a pig 's life is from weaning time until he reaches a weight near 75 pounds. When garbage is to be the sole feed it is a great mistake, and a common one, for the pigs to be weaned while they are very young. The breeder is anxious that the sow shall produce an- other litter as soon as possible, and thus it is not uncommon for weaning to take place when the pigs are four weeks old, or a trifle more. They are then too young to gain well on garbage alone and they are subject to various dietary troubles that are not often observed in pigs weaned later in life. One good litter a year born quite early in the spring and nursed until the pigs are eight or even twelve weeks of age is more profitable than two litters weaned too young. However when warm farrowing pens are provided it is not neces- sary to choose between one litter a year, and two. The sow can nurse her litter the required time and then be bred at the first period of heat fol- HOG CHOLERA AND MEAT INSPECTION 223 lowing weaning of the pigs regardless of the time of year that farrowing will occur. When the pigs are weaned too young "runts" are common among them, and in waiting for the animals to become of sufficient size to receive si- multaneous treatment it is not uncommon for the breeder to prolong to a dangerous degree the in- terval between serum alone and simultaneous treatments. The passive immunity due to the former partially disappears, and hog cholera, fre- quently of an atypical and subvirulent type, some- times appears among them. Often this type of the disease is not recognized as hog cholera. Pigs in large herds require earlier serum alone treatment and are more likely to require two treatments prior to the final serum-virus administration than are those in smaller herds. This is because of the fact that in large herds the chances for infection are so great that the virus of the disease must be regarded as being continuously present. Pasture and abundant room for exercise are of great benefit to young pigs that subsist on gar- bage. There seems to be a general fear that pigs will "run all the fat off them" if they are allowed generous room for exercise. We have repeatedly observed the effects of turning pigs from cramped and dirty quarters into pastures or large enclos- ures, and the change has always been in their 224 HOG CHOLERA favor. Granting good weather conditions, very young pigs that become exhausted in attempts to follow the sow, and feeders near completion of the fattening period are the only exceptions to this rule. There is a tradition that hogs grown on garbage from generation to generation become accustomed to it and consume it to better advantage. For- merly we were inclined to regard this belief as being without foundation on fact, but in later years we have seen evidence that causes us to change our views. It is certain that sows pur- chased from grain-fed herds and required to sub- sist on garbage frequently fail to farrow large litters in the spring subsequent to the change, and while this may often be explained on the ground of insufficient exercise and overfat condition, this explanation covers only a portion of the cases. If we were purchasing breeding animals for a garbage feeding establishment we would regard it of considerable advantage to secure them from herds long accustomed to that kind of feed. Pigs must have dry sleeping quarters or they will not thrive. Due to the excessive moisture in garbage, wet quarters are a common and disas- trous cause of unthriftiness among pigs that sub- sist on it. The greater the run allowed the pigs the easier it is to keep them dry. When the quar- ters are of necessity somewhat crowded, special HOG CHOLERA AND MEAT INSPECTION 225 provisions are necessary or all parts of the floor will be damp. This difficulty can be obviated by constructing overlays consisting of floors of matched material built on two-by-fours laid flat. These are built up around the edges so that in effect they are wide shallow boxes which contain the litter. They should be located as far as pos- sible from the platform where the garbage is fed. What we have said in preceding chapters in regard to maintaining herds immune to hog chol- era applies as well to those that subsist on gar- bage. Young garbage-fed pigs are relatively somewhat slow in getting started, hence they re- quire a little extra care such as we have already outlined. In the absence of this care they are in more or less danger of falling victims to various influences that retard growth, or to ill effects fol- lowing simultaneous treatment administered at a time when they are not in the best condition to withstand it. Garbage Feeding and Sanitary Considerations We have already described the cycle which enables the practice of garbage feeding to aid in perpetuating hog cholera. The ways in which this cycle can be assailed remain to be considered. Our attacks should include efforts to prevent ship- ment from cholera infected herds, gradual revi- sion of our meat inspection regulations with a 226 HOG CHOLERA view to reducing the number of virus containing carcasses that are placed on the market, measures to license and control establishments where gar- bage is fed, and educational activities designed to acquaint breeders with the risks they assume when they feed even a limited quantity of garbage. Measures to prevent shipment from cholera- infected herds may take two forms: first, the al- ternative— prompt serum treatment — should be made available to every breeder, and practicing veterinarians will do well to school themselves in handling hog cholera on the farm, so that the folly of marketing infected hogs will be obvious to the breeder; second, some form of penalty should be attached to the practice. It is obviously impos- sible to reach all offenders but the more flagrant ones could easily be detected, and the effect would be wholesome. When a shipment of swine arrives at the yards containing a considerable number of dead hogs and many others obviously infected with cholera, the chances are that most of the animals in it will produce carcasses which contain the virus. If it could be made compulsory to market such carcasses only in the form of safe but less valuable cooked products, and if the hogs in such a shipment were so tagged and identified that the shipper himself had to accept the conse- quent loss, there would be fewer cholera infected HOG CHOLERA AND MEAT INSPECTION 227 herds marketed, and a higher price for sound ones would prevail. Ante-mortem inspection could at least be made to incriminate an entire shipment containing hogs obviously infected with cholera to the extent of requiring a more severe interpretation of lesions in individuals contained in it. While it is true that petechiae in the kidneys and peripheral hem- orrhages in the lymph glands, for instance, may be due to causes other than cholera, it is likewise true that in shipments such as we have described these lesions are, with negligible exceptions, con- clusive evidence of the disease. License and control of garbage feeding estab- lishments have much to recommend them. Sur- rounding the average city, under present condi- tions, are numerous small herds in which garbage is being fed, and in each one lurks the danger of an outbreak of hog cholera. If a licensing system were in operation, instead of having many un- known sources of infection without any control whatever, we would have a limited number of known sources, in which methods could be so regu- lated as to minimize danger due to spread of the infection. It would be possible to require immu- nization of all hogs fed on garbage — an advantage rather than a burden to the individual feeder — and it would likewise be possible to govern the 228 HOG CHOLERA location of garbage feeding establishments, and to require adequate equipment for their operation. Regulations in Canada require that all men who plan to feed garbage shall first secure licenses, and the plan seems to be working well; princi- pally, we believe, because the sources of danger are limited in number and known. Cooking the garbage is required, but this, in our experience, is a measure of doubtful value. There is no doubt that a boiling temperature will kill the virus, but there is doubt that such a temperature will ac- tually be applied to all garbage fed in any estab- lishment. We have frequently seen neglect of this kind end in disaster. In one instance we were called to handle an outbreak of hog cholera at a large sanitarium where provision had even been made for cooking all garbage under pressure. An unguarded interval during which the apparatus was temporarily out of order was responsible for this outbreak. Immunizing the herd is usually far safer than cooking the garbage on which it is fed, and it has the additional advantage of pro- tecting against all sources of infection. Despite the need for various measures to pro- tect the swine breeder's herd, the fact remains that the measures which he himself can apply will be most effective. He can exclude all pork trim- mings from the kitchen refuse which he feeds, he can discontinue feeding garbage, or he can in co- HOG CHOLERA AND MEAT INSPECTION 229 operation with his veterinarian keep his herd im- munized. Either measure faithfully carried out will protect his herd from cholera infection di- rectly due to garbage feeding. CHAPTER XI CONTROL AND EEADICATION OF HOG. CHOLERA CONTROL of an infectious disease means that rather definite limits have been placed on its spread. Eradication, as applied to a particular area, implies that all the virus which causes the disease has been killed, and that the malady can no longer exist unless it is introduced from with- out. Naturally, in a country in which an acute and fatal infectious disease such as hog cholera is widely disseminated control is the first con- sideration. But eradication is the distant goal, and while our progress toward this goal must at times yield to expediency, there must be no per- manent or long surrender to methods that con- tribute nothing toward the ultimate purpose. Long acceptance of losses due to hog cholera has given us a fatalistic attitude toward the dis- ease. Like the poor, it is always with us and we habitually expect and tolerate it as we expect and tolerate inclemencies of weather or the infirmi- ties of old age. If a foreign infectious swine dis- ease, equally destructive and equally well under- stood, were to appear in this country, even though 230 CONTROL AND ERADICATION OF HOG CHOLERA 231 it were to gain a firm foothold, those whose inter- ests were threatened would demand its eradica- tion and the veterinary profession in cooperation with many breeders — and in spite of the violent opposition of a few — would eradicate it. The first prerequisite, then, is a change on the part of veterinarians, breeders and the public from a passive to an active attitude toward hog cholera. In expressing this view we must not be understood as declaring our faith in a short and intensified campaign against the disease, for the methods that finally succeed will involve details which must grow out of a continual process of trial and adjustment ; but the start must be made, the goal must be kept clearly in view, and con- stant, active and unyielding pressure must be brought to bear on the most obvious practices that serve to perpetuate the disease. During the last four decades hog cholera has caused in this country annual losses ranging be- tween $13,000,000 and $200,000,000, killing annu- ally an average of 66 out of every 1,000 hogs. About once in each decade the disease becomes greatly intensified and in 1887, 1897 and 1914, respectively, the number of hogs killed by it rose above 10 per cent of the country's entire swine population. These are staggering losses, and when one reflects that they will continue indefi- nitely unless intelligent, organized efforts are 232 HOG CHOLEKA made to check them the advantages of such efforts become self-evident. It is not impossible to eradicate hog cholera. The task presents no such difficulties as are en- countered in the eradication of bovine tuberculo- sis, for instance. Hog cholera does not exist long unknown to the owner of the herd it infects; indi- viduals apparently well do not regularly live year after year disseminating the virus ; deaths due to it are rapid and certain and the resulting losses are obvious; it is a foe that strikes in the open. The disease can be stamped out quickly in any herd, and there is an immunizing agent so effec- tive that prompt reporting is the breeder's surest way to avoid loss. When we reflect on the sig- nificance of these facts we may well be led to wonder why the disease does not disappear. The truth is that it does tend to do so, for undoubtedly there are to-day many counties free from the dis- ease that have suffered severely from it in past years, and that will suffer again when the virus once more is introduced from without. When once the virus finds its way into a locality the methods by which it may spread from herd to herd are innumerable but it is time that we direct our attention to the sources of the original infec- tions. We dissipate our energies in trying to con- trol outbreaks of huge proportions instead of concentrating them on the prevention of primary CONTROL AND ERADICATION OF HOG CHOLERA 233 infections. The three most important methods by which hog cholera travels from locality to locality are: 1. Marketing from infected herds. The hogs thus shipped are a menace to others as they are taken to market, they keep stock cars and stock- yards constantly infected, they are sometimes sold from the yards as feeders, and their carcasses are regularly placed on the market in large numbers where they serve to infect many new localities through the medium of garbage feeding. 2. The transportation from public stock- yards of susceptible feeder hogs, and those which receive simultaneous treatment imme- diately prior to shipping. When susceptible feeders are placed in public stockyards they often become infected, and though they leave the yards apparently in good health they soon develop cholera and the farms which receive them become new centers of infection. Feeder hogs that receive simultaneous treatment and which are at once shipped to distant points, frequently ' ' break " as a result, and thus introduce hog cholera into new territory. 3. Wide and indiscriminate use of hog cholera virus in immunizing, especially by untrained men. " Vaccination cholera" is still too common in farm herds, despite the fact that experienced men know how to avoid most of it. 234 HOG CHOLEEA These three practices have essentially the same relation to hog cholera eradication that the feed- ing of uncooked creamery products has to the eradication of bovine tuberculosis. They furnish obvious and wide-open routes for dissemination of the virus. Are they really necessary evils? Are there no possible ways to avoid them? Let us examine the three practices more in detail. Marketing from infected herds. We have al- ready shown that marketing from infected herds is a common practice, that it serves to spread hog cholera virus as the animals are driven to market and when trimmings from their carcasses later find their way into garbage that is fed to suscep- tible hogs. We have also drawn attention to the fact that feeders selected from these herds and shipped to distant points cause many new out- breaks of hog cholera. For our present purpose it remains to review briefly means by which this endless chain of infection can be severed. The first object should be to keep cholera in- fected herds at home. Good local veterinary serv- ice will do much in this direction for it is the ill- advised breeder who ships his infected hogs to market. On the part of the meat inspection serv- ice, rigid interpretations of lesions in all indi- viduals that come from lots obviously infected with hog cholera at the time they reach the yards CONTROL AND ERADICATION OF HOG CHOLERA 235 will serve to discourage shipping from infected herds, provided a tagging system is adopted which will place the losses due to condemnations where they belong — on the man who ships the hogs. The second object should be to prevent the sale of carcasses of infected hogs that reach market despite efforts to keep them away. In other words, carcasses that obviously are carriers of hog cholera virus should not be sold except in the form of cooked products, for hog cholera will be with us as long as the practice continues. We have already mentioned the present deficiency of the federal meat inspection regulations as they apply to this particular point. Whether this de- ficiency is due to lack of authority or to failure to use authority already granted, the effect is the same — many carcasses that show lesions usually considered characteristic of hog cholera are still allowed to pass inspection. It is deceptive to assert, as the regulations do, that these lesions are sometimes due to causes other than hog cholera. Granting, as we freely do, that this is true we still maintain that it is exceptional to such an extent that it should re- ceive scant consideration in the judgment of car- casses that come from lots which contain hogs suffering with cholera when they reach the yards. Hogs that come from infected herds and that show 236 HOG CHOLERA even slight lesions suggestive of cholera will yield carcasses that contain virus, almost without ex- ception. The third object sought should be that of neu- tralizing the effects of virus-carrying carcasses that pass inspection. To this end it should be made known among swine raisers that danger al- ways lurks in the practice of feeding even small quantities of garbage that contain pork trim- mings. A system of licensing garbage-feeding such as the one that now exists in Canada, is also worthy of consideration. Transportation and sale of susceptible feeder hogs and those which receive simultaneous treat- ment just before shipping. Most public stock- yards are contaminated with hog cholera virus, and eventually it should be so ordered that when susceptible hogs enter, it shall be for immediate slaughter only, and the gates shall close behind them forever. Previously we have drawn atten- tion to the fact that " serum breaks " are fre- quently a result of giving hogs simultaneous treat- ment and shipping them immediately afterward. Though this practice is probably the lesser evil as compared to shipping susceptible hogs from the yards without immunization, the fact remains that it is still a potent factor in the dissemination of hog cholera virus. Follow-up treatment as a sub- stitute for simultaneous treatment given immedi- CONTROL AND ERADICATION OF HOG CHOLERA 237 ately before shipping, will do much to minimize this danger, but the ideal will be reached only when feeder hogs are permanently immune to hog cholera before they are shipped long distances. It will take time to provide for an adequate supply of immune feeders so that shipping suscep- tible and recently-immunized hogs from public stockyards will not be necessary, but there are hopeful indications that this will be brought about. Men experienced in the feed-yard even now are eagerly seeking means of avoiding the heavy financial losses associated with "vaccination cholera " immediately following simultaneous treatment and shipping. Among such men there is an active demand for immune feeder shoats, and efforts are being made, though as yet on a limited scale, to supply this demand. The prac- tice of assembling and immunizing feeders, and shipping them only after the resulting reaction is over is already being adopted by some serum companies. This is a step in the right direction, and our belief is that a promising field is open to others who will make a business of supplying the trade with carefully selected cholera - immune feeder shoats. When the supply of these animals is equal to the demand the practice of shipping susceptible and recently-immunized feeders from public stockyards will cease. Indiscriminate use of hog cholera virus in im- 238 HOG CHOLEBA mumzing. When the effectiveness of serum-virus immunization was first demonstrated the demand for these products far exceeded the supply, and hasty preparations were made to produce them in enormous quantities. Enthusiasm for immuniza- tion ran high, and it was looked on as the final solution of the hog cholera problem. Men with- out previous experience with disease and with no fundamental knowledge of the processes that produce immunity were drafted into service to produce and use products potentially capable of doing great harm. It was the accepted belief that all hogs should be immunized, that the process of immunization was a simple one requiring only a low grade of mechanical skill, that serum and virus could be administered without a suggestion of danger, and that the hogs receiving them were from the moment the doses were administered permanently immune to hog cholera. It is little wonder that impotent serum was sent out, that potent serum often fell into unskilled hands, and that some of the laboratories that featured " virus q. s. with all serum orders " sometimes sent out quantities that were just a little more than suffi- cient. The Bureau of Animal Industry laboratory in- spection service with the aid of many far-sighted serum companies has done much to correct these initial evils. The sale of impotent serum for use CONTROL AND ERADICATION OP HOG CHOLERA 239 with virus was much more readily prevented than were the disasters growing out of the use of good serum by untrained or indifferent men, and to- day it is to the latter abuse that most outbreaks of hog cholera which originate from laboratory virus must be attributed. The task of reducing "vaccination cholera" to a minimum must be referred to a trained and awakened veterinary profession. There is an in- sistent demand that vaccination of hogs shall be placed in the hands of laymen, a policy which, if adopted generally, will be disastrous to the swine industry. Yet this demand will be heard — and heeded — as long as there is territory in which there are not qualified veterinarians to do the work. Eeducing the problem of hog cholera control to its simplest terms it may be said that in the indi- vidual animal the disease soon terminates, for the virus will destroy or immunize its host in a few weeks. Likewise in the herd the same principle applies, but if we expand our unit to include county, state or nation the difficulties that present themselves multiply accordingly. The limiting factors in the control of the disease are lack of thoroughly trained men, lack of understanding on the part of the public, and the expense involved. The federal Bureau of Animal Industry has 240 HOG CHOLERA demonstrated that the disease can be kept down in individual counties, but the expense involved was so great as to forbid use of the plan on a large scale. Area work in the eradication of hog chol- era is, we believe, wrong in its conception as long as the virus continually invades the selected terri- tory from without through the three channels that have just been indicated. No successful standardized plan for the control of hog cholera has yet appeared. Killing infected and exposed animals and indemnifying the owners has been tried in England and Canada but results have not been such as to recommend wide applica- tion of the plan. Immunizing all hogs against cholera was once enthusiastically recommended, but we doubt if there can be found to-day an ex- perienced man who considers this method feasible. It would involve the principle of forcing owners to vaccinate, the expense would be prohibitive, and the trained men necessary to carry it out do not exist. In our appraisal of the cooperative forces which can be brought to bear immediately in hog cholera eradication we must include the swine breeder, the practicing veterinarian, the official veterinarian and the serum producer. The breeder should be acquainted with the methods by which hog cholera is spread so as to be able to protect his herd against extraneous CONTROL AND ERADICATION OF HOG CHOLERA 241 infection. He should, with the advice of his veterinarian determine whether his herd is to be maintained immune to hog cholera, or whether it is to remain susceptible and be kept under obser- vation. In case the former plan is adopted the practice of immunizing should not be allowed to lag, and in case the latter seems advisable he should report promptly any infectious disease that appears. The practicing veterinarian's part consists in snuffing out the outbreaks as fast as they appear, in aiding owners to clean up their herds so that they will not serve to infect others in the vicinity, in doing the vaccinating incident to maintaining immune herds, and in advising his clients relative to methods by which their herds can best be pro- tected. Only when the need for police power ap- pears does the province of the practitioner ter- minate and that of the official veterinarian begin. The official veterinarian's primary duty is to bring pressure to bear on the three principal practices that serve to spread hog cholera from locality to locality. By placing restrictions on the sale of hogs from infected herds and from public stockyards ; by a far more severe interpretation of hog-cholera-like lesions in the administration of meat inspection regulations ; by restricting the use of virus so that only trained men may handle it; and by continued supervision of commercial 242 HOG CHOLERA serum laboratories the official veterinarian can play an indispensable part in the fight against hog cholera. The serum producer's part is to supply suffi- cient potent serum to immunize all hogs that ac- tually require immunization. Despite notable ex- ceptions it must be said that on the whole the part has been played well, and when breeders, prac- ticing veterinarians and official veterinarians, as classes, meet their obligations as well as the serum producer is meeting his, there will be far less hog cholera in the country. Volumes could be written on the eradication of hog cholera if we were to follow the various rami- fications into which details of the problem lead us. There are the questions of uniform regulations for interstate shipment of swine ; of separate reg- ulations for crated swine; of rules governing the exhibition of hogs at fairs ; and of funds to admin- ister laws and regulations that are already pro- vided. These and many other supplementary problems appear but consideration of them here would only cloud the more important issues. The points we emphasize in closing are that at the present time the obstacles presented in the eradication of hog cholera rest not so much in lack of machinery to do the work as in the manner in which the existing machinery functions; that three well-known wide-open routes for the inter- CONTROL AND ERADICATION OF HOG CHOLERA 243 sectional spread of hog cholera virus still exist and that they must be closed as the first step to- ward substantial progress in eradicating the dis- ease. Only when this is accomplished can we correctly appraise the lesser task that will yet remain. At present the country's attitude toward hog cholera eradication may be likened to that of a farmer who each year sows weed seeds with his grain, and then labors diligently to eradicate the weeds that spring up. Let us stop sowing the seed. REFERENCES The following references have been selected from the numerous publications on hog cholera because most of them are available to the American veterinarian, and because, as a group, they cover the subject in a fairly complete and satisfactory manner. No attempt has been made to include a complete bibliography. BIRCH, R. R., "Hog Cholera and Its Prevention," Cor- nell Veterinarian, Hog Cholera Number, May, 1916. BIRCH, R. R., "Garbage Feeding and the Care of Gar- bage-fed Swine," Cornell Veterinarian, January, 1918, p. 26. BIRCH, R. R., "Hog Cholera Transmission Through In- fected Pork," Journal of the Am. Vet. Med. Assn., June, 1917, p. 303. BIRCH, R. R., "Researches in Regard to Immunizing Young Pigs, ' ' Report of the New York State Veter- inary College at Cornell University, 1918-1919, p. 73. CAHILL, E. A., "Hog Cholera Control in the East," Journal of the Am. Vet. Med. Assn., January, 1919, p. 314. 244 HOG CHOLERA CAHILL, E. A., "Relative Potency of Tail-bled and Carotid-bled Anti-hog-cholera Serum," Journal of the Am. Vet. Med. Assn., November, 1919, p. 177. CONNOWAY, J. W., "Hog Cholera and Immature Corn," Bulletin No. 74, University of Missouri College of Agriculture. DE SCHWEINITZ AND DORSET, "A Form of Hog Cholera not Caused by the Hog Cholera Bacillus, ' ' Circular No. 41, U. S. Bureau of Animal Industry. DIMOCK, W. W., "Differential Diagnosis of Diseases of the Pig," Journal of the Am. Vet. Med. Assn., Janu- ary, 1919, p. 321. DORSET, BOLTON, MCBRYDE, "The Etiology of Hog Cholera," Bulletin No. 72, U. S. Bureau of Animal Industry. DORSET, McBRYDE, NILES, "Further Experiments Con- cerning the Production of Immunity from Hog Cholera," Bulletin No. 102, U. S. Bureau of Animal Industry. DORSET, M., AND HOUCK, U. G., "Hog Cholera," Farm- ers' Bulletin No. 834, U. S. Department of Agricul- ture. DORSET, M., MCBRYDE, C. N., NILES, W. B., RIETZ, J. H., "Studies on Hyperimmunization against Hog Chol- era," Journal of the Am. Vet. Med. Assn., June, 1919, p. 259. EICHHORN, A., "Present Status of Hog Cholera Con- trol, ' ' Journal of the Am. Vet. Med. Assn., October, 1919, p. 51. FRINK, "W. E., "The Control of Hog Cholera," Cornell Veterinarian, October, 1920, p. 244. HOSKINS, H. PRESTON, "Notes on the Occurrence of Petechial Hemorrhages in the Larynx and Kidneys in Hog Cholera," Journal of the Am. Vet. Med. Assn., July, 1916, p. 478. HOSKINS, H. PRESTON, "Observations on 2800 Pigs In- oculated with Hog Cholera Virus," Journal of the Am. Vet. Med. As