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also on the 14th February. In the course of the next month the blood gave a negative result on examination, and on the 11th March the dog was again inoculated with 4 c.c. of blood from Calf G, after he had been given a primary course of treatment by methylene blue and then by perchloride of mercury-which latter had been in progress five days when, on examination, the blood was still found to be teeming with trypanosomes. Subsequently the dog showed no invasion of the disease, for there was no rise of temperature and no appearance of trypanosomes in the blood, and no signs of the disease were manifest up to the 9th May, which was two months after inoculation with virulent blood from Calf G; from this it was assumed that Dog H had been rendered irumune by the previous injection of blood from Calf D when no trypanosomes could be found in it after the calf had undergone treatment. On the strength of this result, other experiments were conducted both on this dog, as well as on others, of which Dog J (as will be seen later, on page 65), formed a very interesting one.

Subsequent experiment on Dog H.On the 10th May the dog was again inoculated with 9 c.c. of virulent blood from Calf J, which had been treated for three days by injections of perchloride of mercury, but which continued to show trypanosomes in its blood after the injections, and at the same time 9 c.c. of blood from Calf J were inoculated into Dog M as a control to the inoculations of Dog H. During the period of incubation, on the 7th day after inoculation from Calf J, the blood of Dog H was examined, although there was no rise of temperature, but no trypanosomes were found; subsequently from the chart it will be seen that the blood was frequently examined, with a negative result, and that the temperature showed no tendency to rise. On the 19th June the cornea of the right eye became nebulous. In July, although the temperature continued to run normal, the dog fell off in condition. By 15th August the dog looked ill and broke out with a papular skin eruption; became very thin and died on the 21st August.

On Post Mortem.-Dog very emaciated, skin covered with a papular eruption, mucous membranes very pale, liver jaundiced, spleen enlarged, and splenic substance in a semi-fluid condition within the capsule.

Remarks. From the description of this case we note that the blood of Calf D, after a course of treatment by methylene blue and perchloride of mercury, when inoculated into Dog H failed to reproduce the disease with trypanosomes in the blood, and that a subsequent inoculation of blood from Calf G, containing trypanosomes, failed to reproduce the disease in Dog H. It is worthy of note that although the blood of Calf G contained trypanosomes at the time of inoculation the calf had already been subjected to treatment by methylene blue followed by perchloride of mercury for five days. Again, Dog H was inoculated with blood from Calf J, which had trypanosomes in its blood, but this also failed to reproduce the disease it must, however, be remembered that this calf had also been subjected to treatment by injections of mercury for three days. In the case of the first inoculation made it may be that the blood of Calf D had been rendered free from trypanosomes, or that the treatment had lessened its virulence, and so the trypano- somes did not develop in Dog H. In the case of the two subsequent inoculations made from Calf G and Calf J, both of which had trypanosomes in the blood but had both been subjected to treatment by mercury, the failure of development of trypanosomes in the blood of Dog H may have been due to one of two factors, viz. : (a) either the preliminary inoculation of blood from Calf D had conferred some degree of immunity, or (b) that the effect of treatment in the case of Calf G and Calf J had weakened the virulence of the trypanosomes in their blood, and thus inhibited their development in some way in Dog H. Again, both the conditions (a) and (b) may have had a combined effect.

Dog M (see Charts 21a and 21b) was on 10th May inoculated with 9 c.c. of blood from Calf J, which had trypanosomes in its blood, but had been treated for three days by mercury. This inoculation from Calf J was made on the same day as into Dog H, and was to serve as a control over the latter. During the period of incubation (that is, up to the thirteenth day) the blood was examined on no less than six days, but no trypanosomes were found. The temperature, however, showed a very slight rise, which was not like the characteristic rise at the onset of the disease when the blood is first invaded by trypanosomes. On the 23rd when the blood of Dog M was found free from trypanosomes and that the disease had apparently not developed, he was reinoculated with 2 c.c. of blood containing many trypano- somes of Calf L. Seven days later the dog had a rise of temperature, but blood examination revealed no trypanosomes. The temperature again became normal

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and the blood continued free from trypanosomes for nearly a month; then there was again a rise of temperature but no trypanosomes in the blood. After this the tem- perature again became normal, and on the 30th June the temperature observations ceased but the dog was kept under general observations; he fell off in condition in July and later on, the 8th August, he died.

In

Remarks. In this case the first inoculation of blood from Calf J, which had been treated by mercury but had trypanosomes in the blood, proved a failure, for the trypanosomes did not develop in the dog, and, again, the subsequent inocula- tion of virulent blood from Calf L, which had not been treated by mercury, also failed to reproduce the trypanosomes in the dog's blood. It is evident from this that the effect of the mercury treatment of Calf J was to lessen the virulence of the organisms, and so prevent their developing in Dog M, and also had the further effect of preventing the development of trypanosomes in the dog after he was inoculated with virulent blood from Calf L, which had received no treatment. this case relapses of rise in temperature, however, occurred, the dog wasted and ultimately died although trypanosomes never appeared in the blood, so that the trypanosomes in the blood of Calf J and Calf L when inoculated into the dog either altered its phase or died out and formed some toxic material, either of which gave rise to some form of chronic infection which ultimately proved fatal to the dog. That the blood of Calf J contained trypanosomes and was infective to calves is Borne out by the next case of Calf L, which was inoculated with blood from Calf J four days after Dogs H and M, for Calf L developed the disease, showing trypano- somes in his blood, whereas Dogs H and M failed to develop trypanosomes in their blood, so that is evident that the treatment by mercury of Calf J previous to the inoculation of his blood into Dogs H and M had weakened the virulence of the trypanosomes for the dog but not for the calf, for the former failed to develop trypanosomes in the blood, whereas the latter did.

Calf L (see Charts 22a and 22b). This calf, as already stated, was inoculated on 14th May with 8 c.c. blood from Calf J, which had been treated by mercury for three days some time previous to the inoculation. Six days after inoculation Calf L developed trypanosomes in his blood. On the 23rd May 2 c.c. of blood from Calf L was inoculated into Dog M (see page 64) and 1 c.c. of blood into Dog W. This calf was not treated at all and died on the 25th June.

Remarks. This calf served as a control to the inoculations made from Calf J into Dogs H and M, more especially the latter; for when inoculated from Calf J he developed the disease with trypanosomes in his blood, whereas Dog M did not develop trypanosomes in the blood, proving, as described above, that the virulence of the trypanosomes in Calf J had been lowered by mercury treatment for the Dog M but not for Calf L.

Dog J (see Charts 23a to 23h).--This dog was inoculated subcutaneously with 8 c.c. of blood from Horse C, which had been under treatment and had received intravenous injections for six days of perchloride of mercury. At this time the blood of Horse C was examined and found free from trypanosomes. During the incubative period which followed, the blood was often examined, as will be seen from Chart 23a, but a negative result obtained showing that the blood of Horse C was free from trypanosomes or that the mercury had lessened its virulence for the dog. With the idea of trying to make the animal immune against virulent trypanosomes. it was resolved to give the dog a series of daily injections of blood from Horse C. This was begun on the 24th March and continued up to 2nd April. Ten injections were thus given; each injection was from 8 to 10 c.c. in volume, and the total amount of blood injected in the 10 days was 94 c.c. The result of these inoculations was that on the sixth day after the last injection the tempera- ture rose a little. The rise lasted seven days but no trypanosomes appeared in the blood during this incubative period. Subsequently, it will be seen from the chart that no trypanosomes appeared in the blood up to the twenty-third day after the last day of injection with blood. Next day, on the 26th April, Dog J was inocu- lated subcutaneously with 8 c.c. of blood from Calf J, which was suffering from trypanosomiasis, had large numbers of trypanosomes in its blood, and had not been subjected to treatment of any form whereby the vitality of the organisms might have been lowered. Dog J was then carefully watched for the next 15 days; the temperature never rose and no trypanosomes were ever found in his blood. A slight rise of temperature took place on the 12th and 13th April but no trypanosomes in the blood. Subsequently the temperature ran a normal course and trypanosomes were never found in his blood, but by

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