Though milk has often been considered the medium by means of which outbreaks of diphtheria have been propagated, the diphtheria bacillus has only on rare occasions been isolated from the milk in a virulent form.

Cervical buboes preponderate, on the one hand, in naturally infected rats and in guinea-pigs infected by being placed in plague-infected houses and also in rats and guinea-pigs artificially infected with fleas. In rats artificially infected by feeding mesenteric buboes are the most frequent, whereas in upwards of 5000 naturally infected rats in not a single case was a mesenteric bubo present. It may, therefore, be concluded that rats in nature are not infected by feeding on plague-infected material, but probably by the agency of fleas.

1. Antibodies in general are absorbed very slowly from the peritoneal cavity in lower animals, and from the subcutaneous tissues in man and animals. Absorption from the latter is not complete until at least 2—3 days have elapsed.

2. The amount of antibody present at any one time in the general circulation after intraperitoneal or subcutaneous injection is very much less than the amount injected.

3. Clinically, in urgent cases of disease, to inject antibodies subcutaneously is not only to lose 2—3 days' time before the full action can be obtained but to reduce the amount of action that the dose injected can have.

4. By intravenous injection the maximum amount of action is obtained at once.

The whole of the experiments recorded in this paper were made in the Statens Serum-Institut at Copenhagen, where every possible facility was given me for the carrying out of this research. To Dr Thorvald Madsen I desire to express my thanks not only for his unvarying kindliness and courtesy, but also for suggestions and assistance constantly given. I am pleased to have this opportunity of expressing my indebtedness to him.

1. The average capacity of a rat flea's stomach is approximately 0·5 c.mm. On this basis a flea imbibing the blood of a plague rat showing a good septicaemia might take as many as 5000 germs into its stomach.

2. Multiplication of the plague bacillus takes place in the stomach of the rat flea.

3. The approximate proportion of fleas in the stomach of which multiplication of plague bacilli takes place has been determined, and it has been shown that this proportion varies with the season of the year, being six times greater in the epidemic season than in the non-epidemic season.

4. Plague bacilli are present in the rectum and faeces of fleas taken from plague rats, and such faeces are infective to guinea-pigs both by cutaneous and by subcutaneous inoculation.

5. On rare occasions plague bacilli have been found in the oesophagus, but never in any other region of the body, such as the body cavity or salivary glands.

6. During the plague season fleas might remain infective for 15 days after imbibing infective blood, but during the non-epidemic season no animal was infective after the 7th day.

7. A single rat flea may transmit the disease.

8. Both male and female rat fleas can transmit the infection.

9. Experimenting with cat fleas (P. felis) and human fleas (P. irritans), 27 experiments with the former were unsuccessful, and out of 37 experiments with the latter three successes were obtained. Two experiments were made with C. fasciatus: both were successful. Multiplication of the plague bacillus takes place in the stomach of the human flea.

10. The plague bacillus has never been seen in the body cavity or in the salivary glands of infected fleas.

Evidence has been obtained to show that the bite of a healthy flea affords a sufficient avenue for infection by septicaemic blood if it is spread upon the bitten part.

No evidence has been obtained in favour of infection by contaminated mouth parts or regurgitation from the stomach, but the possibility of infection by such means cannot be excluded.

When the blood serum of one animal is injected into an animal of a different species the injected animal in many instances appears to take no hurt. If however after a certain interval the experiment is repeated, it has been noted that the injected animal may speedily show evidence of physical disturbance. Its breathing becomes rapid: its heart-beat grows feeble: its limbs move spasmodically and general convulsions may ensue. These phenomena have been taken to indicate that the injected animal has been supersensitized—or rendered abnormally sensitive—to the serum employed. They may attain such gravity that the animal dies. It has been suggested that the same untoward issue is possible in the case of man, and that the death of patients under treatment for diphtheria is to be apprehended in certain circumstances as the result of repeated injections of antidiphtherial serum, for the reason that the serum in question is derived not from the human subject but from the horse. A suggestion which assails the prestige of the antitoxin treatment of diphtheria cannot be viewed with indifference: it must either be sustained or rejected.

It is well known that when milk is allowed to sour, the rise in acidity is not directly proportional to the increase in the number of acid-forming bacteria. There is a distinct phase in the process during which numerical increase of these organisms takes place, accompanied only by slight acid production, after which the acidity rises very rapidly to a maximum.

Various species of the Order Sarcosporidia, some of which have been studied with great care, infest the muscles of different kinds of birds and mammals. Muscle parasites resembling the one described below do not, however, appear to have been described.

The villages selected for the present series of observations were Dhand and Kasel in the Arnritsar District of the Punjab. They are situated about 10 miles south-west of Amritsar City and within a distance of ¾ mile of each other. They are typical Punjab villages of about 2,000 and 4,000 inhabitants respectively.

Volume VII. p. 470, lines 6 and 34. For “in the Punjab” read “in the Punjab villages of Dhand and Kasel.” In some parts of the Punjab acute human plague occurs in the oflf-plague season.

Case Q, in the same house as case T, in the northern part of Dhand, is marked R in Map 1: it appears as “4” in Map 12. The real case R is in the same house as W on Map 1.

In the present paper we describe the results of further investigations on the life-history of Piroplasma canis in the blood of the dog. In our last paper (x. 1906) we described and figured the movements of the parasite and the mode of multiplication in the dog's blood, and since that time we have confirmed most of our previous observations, and added further facts. The technique of these examinations was fully explained in that paper (p. 604), and it is only necessary to state here that all our later observations on living blood have been made at a temperature of 35°—40°C. The drops of blood were mounted on clean glass slides and cover-glasses kept at this temperature, and were placed as rapidly as possible on the stage of a microscope kept at a similar temperature in a Nuttall's thermostat and examined under a oil immersion lens. In fact we have endeavoured to make our observations in such a manner that the blood should be altered as little as possible.

In the first report (vol. vi. p. 450) we described several series of experiments which had as their object the determination of the relative importance of the Indian rat flea, Palex cheopis, and of actual close contact in the absence of fleas in the dissemination of plague from animal to animal. These observations were carried out in a series of small godowns or cabins, which were built especially for the purpose. The experiments which we have now to put on record are a continuation of those already published. They were carried out during the non-plague season of 1906 and the plague season of 1907.

Since the close of the period which furnished the data for the preceding paper regarding the effects of repeated injections of horse serum, two cases have been observed in the practice of Belvidere Fever Hospital which have special bearing on the subject of abnormal rashes after suitably repeated doses of antidiphtherial serum.

1. Monkeys are susceptible to yaws. The skin eruption in the monkeys I have experimented with (Semnopithecus priamus and Macacus pileatus) is, as a rule, confined to the seat of inoculation but the infection is general, as is proved by the presence of the Spirochaeta pertenuis in the spleen and lymphatic glands.

2. Material obtained from persons suffering from yaws and apparently containing Spirochaeta pertenuis only is infective to monkeys.

3. When the Spirochaeta pertenuis has been removed from this material by filtration, the latter becomes inert.

4. The inoculation of blood from the general circulation and blood taken from the spleen of yaws patients into monkeys may give positive results.

5. The inoculation of the cerebro-spinal fluid of yaws patients gives negative results.

6. Monkeys successfully inoculated with yaws do not become immune for syphilis.

7. Monkeys successfully inoculated with syphilis do not become immune for yaws.

8. By means of the Bordet-Gengou reaction, it is possible to detect specific yaws antibodies and antigen.

9. Yaws antibodies and antigen are entirely different from syphilitic antibodies and antigen.

10. The presence of the Spirochaeta pertenuis in monkeys experimentally inoculated, as well as in yaws patients, is practically constant in the unbroken eruptive lesions; the Spirochaeta is frequently present in the spleen and lymphatic glands.

11. Yaws is generally conveyed by actual contact, but under certain circumstances it may be conveyed by flies and possibly by other insects.

The outbreak of cattle plague in Egypt and the establishment of the Serum Institute at Abbassieh offered a suitable opportunity for investigating some points concerning the nature of the causal agent of the disease, and especially the important question whether the virus is, or is not, capable of traversing a filter candle. On this point the literature is strangely contradictory.

1. During the immunisation of a horse which ultimately failed to yield high grade antitoxic serum, the globulin-content of the total proteid showed no tendency to increase. The slight rise in total proteid which occurred was due to an increase in the albumin fraction. It is probable that the failure of this horse to yield high grade antitoxin was in some way connected with the initial high globulin-content of the serum.

2. During the immunisation of a goat, the rise in total proteid affected mainly the albumin fraction and the globulin fraction in lesser degree.

3. During the immunisation of a horse which ultimately yielded high grade antitoxic serum, the percentage globulin-content of the total proteid, progressively increased. This increase affected the euglobulin fraction more than the pseudoglobulin fraction.

4. In the horse the pseudoglobulin contains the greater part if not all the antitoxin but it seems probable that this relationship holds good only when the antitoxin-content of the serum is steadily rising.

5. In the goat the antitoxin-content of the euglobulin and pseudoglobulin fractions may vary at different periods in the course of immunisation.

The investigations which form the subject of this paper were undertaken at the Pasteur Institute, on the suggestion of M. Mesnil. It is a pleasure to acknowledge my great indebtedness to M. Mesnil for the help and advice he so willingly rendered me whilst I worked in his laboratory. M. Nicolle and he very kindly placed at my disposal their unique collection of colours, which had been supplied them by various firms (notably the Farbenfabriken of Elberfeld). By their suggestions, without which this work would not have been accomplished, they saved me much time and labour. MM. Nicolle and Mesnil had been studying the influence of a large number of colours on various trypanosomes, chiefly Trypanosoma Brucei and to a less extent T. Evansi, T. equinum, and T. Gambiense. Their work was undertaken after the publication of Ehrlich and Shiga's paper on the action of Trypanroth, one of the benzidine colours, on Trypanosoma equinum. M. Mesnil suggested that I should investigate the action of these colours on T. dimorphon which differs in many ways from the above trypanosomes.