a number of herds, themselves free from disease, but located on the borders of infected neighborhoods, were treated by the simultaneous method. Some of these herds became exposed to hog cholera later on, as was shown by the death of the checks. As an example of herds so treated and which later became exposed to disease may be mentioned Nos. 14, 17, 18, 20, and 38. These herds were located in four different neighborhoods and the results were practically the same in. each case. In these 5 herds 201 hogs that were treated by the simultaneous method remained under observation until the close of the experiments; of this number only 3, or about 1 per cent, died, and it is not certain that these had hog cholera, as the owner of the herd to which they belonged stated that in his opinion they did not show hog-cholera symptoms. This herd being at some distance from the Bureau station, no post-mortem examinations could be made. In the same herds there were 38 untreated checks, and of this number 28, or about 74 per cent, died. Had all the animals in these 5 herds been treated, it seems reasonable to suppose that the loss would have been very slight.

In the case of Herds Nos. 22, 31, and 32 the disease-producing blood used in conjunction with the serum did not prove virulent on check animals, and we can not therefore be sure that this blood had any influence upon the production of immunity in these cases. In Herd No. 22 no check animals were used, but of the 60 treated hogs only 2 died. In Herds Nos. 31 and 32, 85 animals were treated, and only 4, or a little under 5 per cent, died, whereas of the 23 untreated checks 18, or 78 per cent, died.

SIMULTANEOUS TREATMENT OF RECENTLY INFECTED HERDS.

As it is sometimes impossible to make a positive diagnosis of hog cholera at the beginning of an outbreak, it may be difficult to decide whether the serum method or the simultaneous method should be employed. In this connection the question has arisen as to whether in the case of herds already affected the use of disease-producing blood is likely to lead to bad results. In order to throw some light on this point the simultaneous treatment was used on infected herds Nos. 4, 6, and 9. The result was apparently the same as in the herds treated with serum alone. In the three herds just mentioned the number of animals treated was 131, and of these, 7, or 5 per cent, died. Of the 18 untreated animals in the same herds 14, or 80 per cent, died. The result obtained in infected herds where simultaneous treatment was employed confirms the results of some special experiments along the same line, and the evidence so far at hand indicates that at the beginning of a hog cholera outbreak either method of vaccination may be practiced with equally favorable results. In cases where the diagnosis is doubtful, the simultaneous method is preferable because of the more permanent immunity it confers,

SUMMARY OF ALL INFECTED HERDS TREATED BY THE SIMULTANEOUS METHOD.

As an indication of what may be accomplished by the simultaneous method in infected herds, there may be cited Herds Nos. 4, 6, 9, 10, 14, 17, 18, 20, 22, 28, 29, 31, 32, and 38. In some of these herds the disease was present at the time of treatment, and in others it appeared subsequent to the treatment. In these herds 539 animals were treated, of which 47, or 8.7 per cent, died. In the same herds there were 108 untreated animals, of which 79, or approximately 73 per cent, succumbed. Four or five of the checks became sick and recovered, but were stunted and worthless, and 9 were sold before disease appeared in the herd. It should be stated that all the loss that occurred among the treated hogs took place in herds where disease existed at the time of treatment.

It seems evident that the simultaneous treatment is indicated (1) when it is desired to immunize healthy hogs for a longer period than a few weeks, (2) in herds where infection is suspected but regarding which some doubt may exist, and (3) in infected herds where there is a probability that some of the animals may not become exposed and there is danger that the transient immunity which the serum alone imparts may be lost.

CAN DISEASE BE STARTED IN HEALTHY HERDS BY THE SIMULTANEOUS TREATMENT?

This question is an important one, and was given early consideration in the experimental work at the Bureau station. It was shown in Bulletin 102 that hogs are not injured by the simultaneous injections when a sufficient dose of serum is administered with the virulent blood. It was also shown that in those cases where the dose of serum was not sufficient to protect the treated animals completely, symptoms of disease developed more slowly, the disease was much milder in its course, and it was not communicated to other hogs unless the treated animals became quite sick.

As 20 c. c. of hyperimmune serum given simultaneously with 2 c. c. of virulent blood had proved satisfactory in the experimental tests for pigs weighing from 25 to 75 pounds, approximately the same amount of serum was used at the beginning of the field tests. In Herd No. 2 this dose was used for pigs weighing 75 pounds, and in Herd No. 4 the same dose was used for shotes weighing as much as 100 pounds. In both instances the animals were protected against the 2 c. c. of disease-producing blood. In the case of Herd No. 6, which received the simultaneous treatment, the herd also had some natural exposure to disease, but the serum protected against the 2 c. c. of virulent blood as well as against the natural exposure,

except in the case of 3 animals which were probably infected before treatment was carried out. In Herd No. 8, where the animals were given the same doses of serum and disease-producing blood, the simultaneous treatment also gave entirely satisfactory results.

In Herd No. 11, however, where the treated animals were not large and apparently not more susceptible to virulent hog cholera than usual, the simultaneous treatment was followed by the appearance of disease. Nine days after treatment 2 or 3 of the shotes became droopy and later died after exhibiting the usual hog-cholera symptoms. Autopsies on these animals showed the usual hog-cholera lesions. As the herd contained only 1 untreated pig, and this could not be identified, it could not be determined whether the disease in this instance was readily communicable to healthy shotes or not. As will be seen from the herd records, the loss in this herd was comparatively light. There can be no question as to the potency of serum No. 2, and the virulent blood was the same as that used in some of the other herds with satisfactory results. It would seem that the animals in Herd No. 11 were either unusually susceptible to disease or else some unknown factor was present which in some way influenced the results.

In Herd No. 14 very large shotes, weighing from 125 to 160 pounds, were treated by the simultaneous method with satisfactory results. In Herd No. 17 shotes weighing 100 pounds were also given the same treatment with no indication of trouble, but in Herd No. 16 much smaller shotes were apparently made sick by the simultaneous treatment. However, in this herd the loss was small considering the number of animals involved. In but one other herd did disease appear to have been started by the simultaneous treatment. This was No. 21, where an old hog became sick about one week after injection and soon died, an autopsy revealing hog-cholera lesions. Two shotes in this herd also seemed sick, but recovered after receiving an injection of serum. Many other herds received the simultaneous treatInent, but showed no indication of disease as a result.

The prompt re-treatment of the three herds, Nos. 11, 16, and 21, with serum alone was sufficient to prevent serious loss. In Herd No. 21 only 1 animal out of 74 died. This indicates, in the opinion of the writer, that, if disease is started in a herd, by the simultaneous treatment the loss will be of little consequence if the herd is carefully watched and reinjected with serum as soon as the first indication of trouble appears. The evidence so far at hand goes to show that the result obtained with Herd No. 11 will be met with very infrequently and the loss resulting from the simultaneous treatment will be so slight as not to be a serious objection to its use.

PREVENTING THE SPREAD OF A CHOLERA OUTBREAK BY VACCINATING AROUND ITS BORDERS.

Owing to lack of time and to the large amount of hyperimmune serum that would have been required, experiments for gaining information on this point were carried out in but one neighborhood. The appearance of disease in Herd No. 10 constituted a new center of infection, and it was decided to vaccinate the neighboring herds with a view to stamping out the disease in that locality; consequently all of the hogs in Herds Nos. 19, 22, 26, 27, 30, 33, and 34 were treated, no checks being left. These herds were all well when treated and continued so, with the exception of No. 22, which was showing indications of disease when vaccinated. The disease soon died out in this neighborhood, and it is impossible, therefore, to say whether or not the result would have been the same had the herds been left untreated. The disease in Herd No. 10 was not very virulent, but the appearance of cholera in No. 22 would indicate that but for the use of the hyperimmune serum the disease would probably have appeared in some of the other neighboring herds. As the serum used in these experiments was known to be potent, we have every reason to suppose that the herds in question would have been effectively protected against hog cholera had the disease in No. 10 been as virulent as that in some other neighborhoods.

While, therefore, we did not carry out extensive experiments as to the limiting of outbreaks of hog cholera by the use of serum, we nevertheless have reason to believe, judging by the results in this instance and by what was accomplished in individual herds, that outbreaks may be prevented from spreading and that the disease may even be stamped out by the prompt use of serum when new centers of infection are discovered.

EFFECT OF VACCINATION ON ANIMALS OF DIFFERENT AGES.

While a majority of the vaccinations herein recorded were made on spring shotes, a considerable number of old hogs (animals from 1 to 3 years old) and quite a number of sucking pigs were treated in the different herds.

In the experiments with old hogs the number of checks was somewhat limited, as the owners were loath to leave any of them untreated on account of their greater value. In a number of herds, however, it was shown that old hogs were protected by the treatment, while the untreated ones died. Such was the case in Herds Nos. 10, 20, 29, 31, 35, and 42. In the opinion of the writer old hogs can be as successfully vaccinated as shotes.

As the field tests described in this article were carried out during the fall of the year, when as a rule there are but few sucking pigs, only a limited number of young pigs could be treated. However, in some herds where disease had recently appeared very striking results were obtained by treating a part of a litter and leaving the remainder untreated as checks, as is shown in the case of herds. Nos. 31 and 35.

The results obtained in the various herds which were treated would ⚫ certainly indicate that hogs of any age may be successfully protected against hog cholera in its various forms, whether mild or virulent, by a sufficient dose of hyperimmune serum.

CONCLUSIONS.

1. The serum of properly hyperimmunized hogs, when administered in sufficient doses, will protect nonimmune hogs of all ages against hog cholera. As indicated in the experiments which have been described, the following approximate doses should be used: For sucking pigs, from 10 to 15 c. c.; for shotes weighing from 30 to 200 pounds, from 20 to 30 c. c.; for old hogs, from 40 to 60 c. c. Later experiments, however, will probably show that as much as 60 c. c. is never required..

2. Healthy herds treated by the simultaneous method are rendered immune against hog cholera.

3. In herds recently infected with hog cholera, where only a few animals have become sick, nearly all loss may be prevented by the use of serum alone. The serum will not save those animals in the last stages of the period of incubation, but may be depended on to protect all of the uninfected animals and most of those in the early stages of the period of incubation. Simultaneous treatment in these herds appears to yield the same results as the serum when given alone except that the duration of immunity may be longer.

4. In badly infected herds, where the disease has made considerable headway, a number of the animals may be saved by the serum, the percentage saved depending upon the extent of the infection; that is, upon the number of unaffected or only slightly affected animals in the herd at the time of treatment.

5. By the prompt use of hyperimmune serum in an infected herd and the prompt vaccination of surrounding herds, hog cholera may be quickly stamped out when it first appears in new territory. In case the infection has already spread from one infected herd to several neighboring herds, the vaccination of all herds bordering on the infected area will prevent further spread of the disease.

6. The treatment of healthy shotes by the simultaneous method very rarely causes the appearance of disease, and should it do so it may be quickly controlled by the subsequent use of hyperimmune serum alone.