Fatal general infection can be readily production in mice by spraying with pneumococcal culture in a closed chamber without resorting to any artificial means of lowering the animal's resistance.

In the experiments recorded the proportion of unprotected mice which developed septicaemia varied considerably, the highest being nine out of ten. These irregularities may be partly attributable to variations in (1) the fineness of the spray, and (2) the virulence of the culture.

In unprotected mice death from septicaemia rarely occurs before the 3rd day after spraying and may be delayed for a week or more.

Vaccination by subcutaneous and intraperitoneal inoculation with heated cultures afforded protection against infection by inhalation to 11 out of 13 mice. Two succumbed to septicaemia although they had resisted 14 days earlier an intraperitoneal dose of 0·0001 c.c. of culture. The culture used for spraying was evidently in a highly virulent state since nine out of the ten controls died of septicaemia.

The above experiments were with homologous cultures but tests have also been made of the efficacy of vaccination against heterologous strains. For example, vaccination with Types I and II cultures gave apparently a certain amount of protection against infection by spraying with a mixture of Type III and Group IV strains.

Passive immunity induced by an injection of antipneumococcal serum immediately before spraying was effective against the homologous types in all of a batch of 13 mice. The resistance showed a tendency to diminish with the lapse of time, since on re-spraying the same lot of mice 3 weeks later one mouse developed septicaemia.

In unprotected mice where death was delayed for some days after spraying there was generally no evidence to the naked eye of any local pulmonary lesions. Rarely typical grey consolidation of portions of the lungs was found. A pneumonic condition occurred more frequently in mice in which a slight degree of immunity had been produced. For example, a Type II pneumonia was found in a mouse which had been immunised against Type I.

The production of the carrier state is a regular sequel to spraying even with the most virulent cultures of pneumococci. A large proportion of the mice which survived spraying were nasopharyngeal carriers a fortnight later and the condition persisted in one mouse for 99 days. A carrier of pneumococci may succumb to septicaemia 15 days after the date of infection; it is not known whether any immunity develops in carriers.

The presence, about the pharynx of mice, of Gram-negative bacilli which grow rapidly in culture and are of high virulence when introduced parenterally is a source of difficulty in attempts to demonstrate pneumococci.

An attempt was made to ascertain whether, after spraying, nasopharyngeal carriers of pneumococci were more numerous among normal or among protected mice. The results were inconclusive, but there was no marked indication in the experiments recorded that the state of immunity influenced the carrier condition.

The present investigation deals with the routine bacteriological examination of 525 samples of water, 265 of which contained lactose fermenting bacilli; 1441 strains were isolated and various differential tests were used in the classification of these organisms.

All the strains were tested in dextrose phosphate culture for the methyl red and the Voges and Proskauer reactions, and although most of them gave normal results (M.R. + V.P. 0 or M.R. 0 V.P. +), there were 25 strains, 1·73 per cent., which gave either double positive or double negative reactions. Similar cases have already been discussed in an earlier portion of this paper, and they leave no doubt that there are types which may vary from the normal as far as the methyl red and the Voges and Proskauer reactions are concerned. At the same time these abnormal types are not sufficiently numerous to make any real practical difficulties in the use of these tests for routine purposes.

The Koser test, considered by many bacteriologists to be of great differential value, was found to give imperfect correlation with the other reactions.

1395 strains were isolated which could be classified in the B. coli group as a result of the production of acid and gas in lactose, the clotting of milk, and the non-liquefaction of gelatine, but when the methyl red and the Voges and Proskauer results were considered it was found that nearly 11 per cent. of these strains were of the B. lactis aerogenes type, and were therefore of no value as indicators of faecal pollution.

The indol reactions were somewhat variable. Among 1244 strains of the B. coli type (M.R. + V.P. 0), more than 10 per cent. failed to produce indol; while among 151 strains of the B. lactis aerogenes type (M.R. 0 V.P. +), nearly 51 per cent. were indol producers. Preliminary extraction with ether was carried out with 448 of these strains before Böhme's reagent was added. With this technique it was found that among 400 methyl red positive types there were 87 strains (22 per cent.) which produced no indol, and among 48 methyl red negative strains there were 12 (25 per cent.) which gave the reaction. Chen and Rettger (1920) were unable to establish any definite correlation between the indol test and the other reactions.

When the sample results were studied, it was found that although 262 waters contained organisms which were included in the B. coli group on the basis of the lactose, milk and gelatine tests, nearly 6 per cent. of these samples contained only organisms which gave a methyl red negative, Voges and Proskauer positive reaction, and were probably associated with pollution from soil washings rather than contamination from faecal sources. This means that the application of the methyl red and Voges and Proskauer reaction does make a considerable practical difference in the interpretation of results in the bacteriological examination of water.

More detailed examination as regards the fermentation of the various carbohydrates is useful for purposes of classification, but is of no significance, in the light of our present knowledge, in assessing the probability of excretal pollution.

It is suggested that, in considering the results of a bacteriological examination of water, organisms should be regarded as significant which are of typical morphology and staining reaction, produce acid and gas in lactose, fail to liquefy gelatine, clot milk, and give a positive methyl red and a negative Voges and Proskauer reaction. The production of indol in a medium containing peptone may be added as an extra test if desired, but the available evidence does not suggest that failure to produce indol is a sufficient basis for the exclusion of an otherwise typical bacillus from the B. coli group.

My thanks are due to Dr G. D. Dawson, in conjunction with whom the present investigation was started; and also to Prof. W. W. C. Topley whose interest throughout the course of the research was made manifest by his helpful advice and criticism.

Except in the West Australian pearl fisheries most of the world's diving is done in shallow water, from small boats or piers; and in civil life each diver is independent and controls the situation according to his own lights. In the British Navy the divers work under an officer who directs all the above-water side of things, such as the arrangements for pumping down air, and deciding whether or not it is safe to dive in existing circumstances. Though the officer will have had a short training at the Naval diving school he is not necessarily experienced in under water work; but he will be a seaman possessing knowledge of boat management, weather, and tides, with the authority to give and enforce orders which the young diver lacks. For simple shallow water work the first system is probably the better, though hardly practicable in a disciplined service where the divers are recruited from the lower ratings.

In connection with recent investigations on the spread of bacterial infection among mice, the possible effect of variations in the virulence of the infecting organism has, inevitably, formed one of the problems for study.

Since Dick and Dick (1924) Published their method of testing the susceptibility or insusceptibility of human beings to scarlet fever various other workers have reported in vestigations which have confirmed the observations of the Dicks.

The inhalation of coal and stone dust, as used in collieries, by pit ponies produces no permanent lesions of the lungs.

The dusts accumulated in the lung continue to increase during the first two years of exposure (approximately), but the rate of elimination then becomes equal to that of absorption.

The dusts accumulate, probably in the lymphatics, firstly around the blood vessels, secondly around the bronchi, and thirdly in the deep layers of the pleura.

The dusts accumulate in greater amount around the smaller blood vessels and bronchi than around the larger ones.

There is a greater deposition of dust near the pleura than deeper in the lung substance.

The dust is eliminated via the bronchi and the lymphatics.

Dust accumulates in the lymph glands and spleen. In the former, at least, it is largely intracellular.

Excessive stone-dusting causes extra accumulation of dust within the lung: this, however, causes no fibrosis.

All forms of the soft pit stone used were equally harmless.

The normal horse's lung contains very little dust.

General interest was first aroused regarding the respective powers of the human and bovine types of the tubercle bacillus to infect the human subject by the address of Koch at the Tuberculosis Congress in 1901. In this he stated that the two types produced different diseases, and that the amount of human tuberculosis due to infection by the bovine type of the tubercle bacillus was negligible.