During the period July 1st—October 31st, 1911, 15,332 rats were examined for plague infection. These rats were obtained (see Map facing p. 311) partly from the area which in the previous year had been found to be infected with rat-plague and partly from the districts immediately adjacent to this area.

As a result of the present enquiry 27 farms or other premises were found to harbour plague-infected rats.

These 27 places are all within the area previously pronounced to be infected. No plague-infected rats have been discovered outside this area.

Experience of rat collection during the present enquiry showed that the rat destruction which had been maintained by local enterprise since the end of 1910 had in many localities appreciably diminished the rat population.

In a former paper on the inactivation of the haemolytic complement by means of shaking (1913), I considered it possible that the process of shaking-inactivation might be explained by assuming that an adsorption of the complement occurred on the surfaces of the precipitate, which is always found when a serum is shaken. I was unable however either to fix the complement of a fresh serum by adding the centrifuged coagula of a shaken serum or, on the other hand, to set free a complement presumably adsorbed on the surface of precipitated proteins, which are found to be soluble only in alkali. I therefore had to leave undecided the question as regards the nature of the process of shaking-inactivation.

Until recently there has been a general impression among a large proportion of the local medical faculty in Jerusalem that enteric fever was very uncommon and that typhus fever was practically unknown. As we are now basing our diagnosis of malaria increasingly upon the discovery of malarial parasites in the blood, we find that while on the one hand many of the most severe malarial infections, especially those with subtertian parasites, have little or no pyrexia, on the other hand, many cases which we should have called “ remittent malaria” or “malignant malaria” or “typho-malaria” in years gone by, are proving to be of other origin. A case of remittent pyrexia which does not yield in three, or at the outside five, days to efficient dosing with quinine is not in our experience a pure malarial infection.

In view of its possible relation to the epidemiology of plague, a knowledge of the biology of the common rat-flea of England, Ceratophyllus fasciatus Bosc, is much to be desired, and therefore, at the request of Professor Niittall, the present investigation was undertaken. The observations recorded below are mainly the result of experimental work with fleas conducted in the Quick Laboratory, Cambridge; but before proceeding to a description of the experiments it is considered advisable to give a short summary of the life-cycle of the rat-flea.

In the Berkefeld filtration of a fresh guinea-pig serum, adsorption on the filter surface takes place, and the serum passes unaltered, if the saturation of the adsorbing surface has become complete.

This adsorption involves most probably first the albumins, which process then secondly influences the filtrability of the globulins. It is also shown that the physical conditions of the serum as regards salt concentration and dilution as well as H.-concentration modify the effect of filtration to a large extent.

It is shown that provided the total number of individuals exposed to a constant environment which is inducing change within them be constant, and the number of units of change which must take place within any given individual in order to cause a given event be also constant, then the number of these events is a quantitative measure of the extent of the change in all of the individuals taken together.

From this it follows that the results of Madsen and Nyman and of Chick may legitimately be regarded as proving that the process which underlies disinfection obeys the time-relations and other characteristics of a mono-molecular chemical reaction.

1. Pigeons fed on daily rations of polished rice equal to 1/20th their initial body-weight develop symptoms of polyneuritis in about three weeks and usually lose considerably in weight.

2. The efficacies of various ox-tissues for preventing polyneuritis have been determined, and the tissues arranged according to their anti-neuritic powers are in the following descending order: liver, cardiac-muscle, cerebrum, cerebellum, voluntary muscle, and (cows') milk.

3. Alcoholic extracts of the excreta of a hen fed on unpolished grain and of the faeces of a rabbit fed on bread and cabbage cured polyneuritis in pigeons. The whole content of anti-neuritic substances present in the dietary was therefore not absorbed or else some amount is synthesised by the bacteria of which the faeces consisted to a considerable extent. No conclusions can consequently be drawn as to the actual distribution of the active substances in the animal body, until the extent to which the various tissues are absorbed from the alimentary canal of birds has been determined.

4. Nuts (husked filberts) are very efficient in preventing polyneuritis, being even superior to lentils and husked barley. Cheddar cheese, on the other hand, even in considerable amount, has no preventive effect.

5. Malt extract taken from two different samples readily cured polyneuritis in pigeons. A third sample however even in large doses had no curative action.

6. For the prevention of beri-beri egg-yolk, heart-muscle, liver, nuts, barley, and lentils can be recommended as suitable foodstuffs with which to supplement the polished rice diet. As meat (voluntary muscle) has been frequently found to be ineffective in preventing epidemics of beri-beri, its replacement by heart and liver in mixed diets would be a considerable improvement, because, not only are these tissues when suitably prepared as nutritious as voluntary muscle, but they also contain the anti-neuritic substances in much higher concentration.

On June 30th, 1911, we proceeded to Ipswich, with instructions from the Local Government Board to assist in an enquiry, the purpose of which was to determine the extent of the plague epizootic amongst rats in the surrounding districts. The share of this work allotted to us consisted in examination, at the Municipal Laboratory, of the animals received, and in selection, for further investigation by the Board's pathologists in London, of material which appeared suggestive of plague. For this purpose, rats presenting features in any degree consistent with the presence of plague were regarded by us as suspicious.

Interesting results were obtained with cultures in ammonia agar, from them it is evident that the nitroso-bacterium grows readily through this medium whether inoculated on the centre of a plate or when covered with the agar jelly itself. Further, the presence of 5 to 10% of beef broth in the ammonia agar allows of better development.

Potassium phosphate agar containing bouillon gelatine but no free ammonia, on being inoculated with cultures of nitroso-bacteria, also developed nitrification; the organic matter was broken down, ammonia formed, and nitrites built up.

Nitrification in ordinary bouillon agar plates shows that organic matter does not necessarily form a barrier to the process; and further, that two of the cultures had only been fed with inorganic salts for three and four years respectively prior to the inoculation into the plates, is good evidence that gradual additions of organic matter are not absolutely necessary.

Calcium sulphate blocks allowed me to work with a larger amount of very active culture: from these it was found that urine was a very good culture medium indeed. Also that peptone water diluted with water, or peptone beef broth, milk, or blood serum diluted with ammonium sulphate could be used as culture media; sometimes these checked nitrification for a time but it afterwards became well established.

The experiments with undiluted urine were wholly successful and stand as a further proof of nitrification in presence of organic matter.

From these results it is clear that the nitroso-bacterium is a very powerful nitrite-forming micro-organism, that it is not readily destroyed, and that a certain amount of organic matter is essential to its greatest development, but for this a large amount of culture must be used.

In conclusion I have to offer my deepest thanks to Sir William Power for the great help that he has given me and for the kindness that he has always shown; also to others who have most kindly advised me my grateful thanks are due.

(1) Chickens fed on a 1/20th their body-weight daily of padi, cured or parboiled unpolished rice, or fresh (partly polished) rice, remain free from polyneuritis for at least 28 to 100 days.

(2) Chickens fed on the same ration of polished Siam rice develop symptoms of polyneuritis in from 20 to 70 days.

(3) When the polished rice is soaked in excess of water for 24 hours the birds succumb to polyneuritis in from 10 to 35 days; when the rice is soaked for 48 hours the disease appears still more readily, viz. in 15 days.

(4) Chickens fed on 1/20th their body-weight of parboiled rice which had been soaked for 24 hours also develop polyneuritis in from 13 to 39 days. This fact is of practical importance, as epidemics of beri-beri have been traced to the practice of soaking unpolished rice prior to cooking and discarding the water.

(5) Although birds fed on diets of polished rice, sago, or glucose develop polyneuritis, when fed on commercial starch they often fail to do so and merely lose considerably in weight. An explanation is offered.

(6) While fowls fed on 1/20th their body-weight of padi remain free from polyneuritis for at least 60 to 100 days, when this ration is supplemented by 1/6th the body-weight of washed unpolished rice or 1/10th of polished rice polyneuritis appears in from 20 to 30 days.

(7) On the other hand, chickens fed on rations varying from 1/5th to 1/30th of their body-weight of washed unpolished rice develop polyneuritis in about the same time, 10 to 20 days.

(8) On dietaries composed of rations of polished rice varying from 1/20th to 1/40th the body-weight and of yeast varying from 1/2500th to 1/3500th the body-weight pigeons and chickens do not develop polyneuritis until at least 32 to 100 days have elapsed, but when the carbohydrate ration is doubled by the addition of polished rice or sago the birds fall ill in from 13 to 46 days.

(9) Even when daily rations of polished rice as large as 1/10th the body-weight are fed to chickens together with varying amounts of yeast, 93 to 98 per cent, of the carbohydrate is digested and absorbed and the excreta contain no anti-neuritic substance. This shows that the rapid development of polyneuritis induced by feeding large rations of starch is not due to interference of undigested carbohydrate with the absorption of the active material.

(10) Intestinal bacteria, unlike yeast, contain little anti-neuritic substance.

It having been considered desirable that further experiments upon the range of flight of flies should be carried out, the investigation of the subject was entrusted to Dr E. Hindle and Mr G. Merriman, who are engaged in research in my laboratory. Although the experiments here recorded were carried out under somewhat adverse climatic conditions, they appear of sufficient interest to warrant publication, since the results with regard to the influence of wind seem to run counter to those recorded by previous workers, and also, apart from Hewitt's work referred to below, data have hitherto been wanting in respect of the range of flight of flies (Musca domestica Linn.) in towns. The simple graphic method of recording the results of the flight experiments, which occurred to me during the course of the work, may commend itself to others who may carry out similar investigations in the future.

The subject I propose to discuss in the present and subsequent papers is of importance in two ways. Popular traditions have frequently implied that the age at which a parent begets offspring is not without influence upon the characters of the latter, the prevailing belief being humorously portrayed in the late W. S. Gilbert's ballad “The Precocious Baby.” Again, recent thinkers, notably Professor Karl Pearson, have asserted that elder born children differ markedly in liability to certain diseases from their younger brethren. Were this view to be accepted it would be relevant to enquire whether the difference might not be a function of the age of the parents at the time of birth of the offspring or at least whether such difference might not play a part in bringing about this result. Assuming that any such effect could be demonstrated, it is plain that a valuable stimulus would be given to the study of physiological changes in the reproductive system within the fertile period. These are the immediately interesting aspects of the subject, but with them I am less directly concerned than withcertain secondary consequences.

It is well known that typhoid bailli, freshly isolated from enteric fever patients, vary in their capacity to undergo agglutination. The following series of experiments was carried out with the object of discovering whether these differences in agglutinability are dependent on the stage of the disease at whih the bacillus is isolated, or on the body substance from which it is obtaind.

Under the conditions of our experiments, indication was afforded that—

(1) House-flies tend to travel either against or across the wind. The actual direction followed may be determined either directly by the action of the wind, or indirectly owing to the flies being attracted by any odours it may convey from a source of food.

(2) It is likely that the chief conditions favouring the dispersal of flies are fine weather and a warm temperature. The nature of the locality is another considerable factor, as in towns flies do not travel as far as in open country, this being probably due to the food and shelter afforded by the houses.

(3) Under experimental conditions, the height at which the flies are liberated, and also the time of day, appear to influence the dispersal of the insects. As judged by one experiment, when flies are set free in the afternoon they do not scatter so well as when liberated in the morning.

(4) The maximum flight in thickly-housed localities in our experiments was about a quarter of a mile; but in one case a single fly was recovered at a distance of 770 yards. It should be noted, however, that part of this distance was across open fen-land.

1. Sera and antisera when kept in the dark at room temperature sealed in glass tubes occasionally give specific reactions after a period of 12 years. In most cases, however, negative results were obtained with the antisera, whilst in others the reactions were non-specific.

2. Fowl blood will still give specific complement fixation and precipitin reactions after being in the alimentary canal of either Argas persicus or Ornithodorus moubata for at least 23 months. The gut contents of Pediculus vestimenti fed on man three days previously, also will give specific reactions with human antisera.

Attention was first directed to the presence of a substance in milk acting as a complement by Pfaundler and Moro(1) and from that time onwards there has been much conflicting evidence published on this subject. Kopf(2) stated that complement could not be demonstrated in milk, using the method of Pfaundler and Moro, and the work of Sassenhagen and Bauer(3) would seem to show that complement is not present in milk unless the milk of cows suffering from mastitis be present. Sassenhagen(4) in a later paper states that complement is present in the colostrum of cows and goats and that it disappears as lactation progresses. Lane-Claypon(5) has followed Pfaundler and Moro and states that complement can be found in almost any milk.

The diagnosis of bubonic plague in rat cadavers, the examination of which is a recognised method of prophylaxis for ships or other communities, which may have been in contact with endemic centres, is attended by especial difficulties, and, on the other hand, calls for especial speed and finality in technique.

The collections of fleas described in this paper were made during an enquiry into the plague conditions of Upper Egypt, carried out in 1912 and 1913 on behalf of the Egyptian Government. With few exceptions the fleas were taken from rats or other rodents trapped either in the native houses or in the Nile boats (native river craft), which were infested with rats.

Whether the vaccine virus is filterable or not has been the subject of experiment and discussion for many years and since Negri's results published in 1905, from which he deduced that the virus was filterable, numerous experiments dealing with the subject have been made by many workers.

In the course of our investigations on the biology of flies, during the year 1912, a certain number of experiments were performed in order to ascertain whether house-flies possess any colour preference. In the case of mosquitoes, Nuttall (1901) has shown that these insects have a very well-defined preference for certain colours. When a number of boxes, lined with different coloured materials, were placed in a tent containing mosquitoes, the latter occurred most frequently on navy-blue, and, in descending order, on dark red, brown, scarlet, black, slate-grey, dark green, violet, leaf-green, blue, pearl-grey, pale green, light blue, ochre, white, orange, and yellow. Very few insects indeed were found to rest on the last seven colours.