A form of ultramicroscope apparatus is described which enables the evaporation of mist droplets to be followed for long periods. A rough method of estimating the size distribution in aerosols is also given.

The rates of evaporation of particles of various phenol solutions have been studied, the solutions chosen being of possible interest as aerial germicides. It is shown that the typical evaporation curve for a binary mixture consists of three parts, which in actual cases need not all be present. Sometimes the more detailed history of an evaporation can be deduced from the results.

The approximate effective size distributions in mists of hexyl-resorcinol—propylene-glycol solutions have been measured and compared with the evaporation rates.

It is shown that the efficiency of aerial germicides is partly a function of their volatility, and three rough classes are distinguished. But biological evidence is adduced which suggests that the solubility of the germicides in water may be of equal importance, and that the liquid in which the germicide is dissolved is not without effect.

A centrifuge is described which enables the maximum particle size in a mist to be limited to a desired value.

Methods of estimating quantitatively germicidal aerosols are discussed, and a method described which has been found to give reasonably accurate results in practice. Tentative experiments have been made to determine whether the materials studied are likely to cause corrosion of metals, etc., after pro-longed use.

The collision theory of aerial disinfection is discussed, as is also the applicability of Langmuir's treatment of the evaporation of fine particles in mixtures.

The development of the experimental technique involved in the biological investigations appertaining to air disinfection has been discussed, together with the numerous fallacies arising and the means by which these have been overcome.

The construction of a special pair of experimental chambers is described, and details given, both as regards the bacteria and germicides, of the exact experimental conditions under which the most consistent results can be obtained.

The requisite characteristics of germicidal mixtures which could be utilized for air disinfection are considered, and examples of suitable germicides and solvents are given. The method of recording and evaluating the results of a varied assortment of experiments is explained to facilitate inter se comparison.

Examples are given of the lethal effectiveness in the air of several germicides in broth emulsions, both with and without the presence of serum, on stock cultures of selected types of bacteria. The sensitivity to the germicides of the bacteria making up the flora of the average normal saliva is compared with that of broth emulsions of bacteria.

10% hexyl-resorcinol dissolved in propylene-glycol+0·05 % sulphonated lorol (“S2”) was the most effective all round germicidal mixture of those tested. Various other germicides were found equal in germicidal activity in the air, but for reasons stated have been deemed unsuited for use in the presence of man.

The relationship between germicidal efficiency in the air and mist particle size and persistence has been studied by means of centrifuged mists. Particles of 0·5–1·0μ radius are shown to be the most useful in dealing with bacterial particles containing organic matter. Laboratory cultures, emulsified in broth, have been sterilized in mist dispersions by droplets of bactericides at least as small as 0·25μ radius.

Tests on the penetrating abilities of bactericidal mists and bacteria through certain cloths have been performed.

Experiments to demonstrate the surface sterilizing properties of aerosols have been performed, and examples of differences in effect on horizontal and vertical surfaces are noted.

The degree of tolerance of man and animals (mice) for a number of phenolic substances and some organic solvents has been compared with the degree of tolerance of bacteria for the same substances.

The tests on man have been confined to the detection by the special senses of the substances suspended in the air as a fine mist.

The tests on animals were designed to show acute and chronic effects, the results being recorded in terms of clinical symptoms and pathological changes in the organs. A record was also kept of the findings as regards protozoal parasites of the host, and compared with the normal incidence among ordinary laboratory stock.

Tests on bacteria were instituted for the purpose of gaining information on the host-parasite tolerance ratio for our germicides when in the air and when in the test-tube.

1. Sulphapyridine is an efficient prophylactic or therapeutic agent against intradermal infection with the strain of Vibrion septique selected for test, whereas, in intramuscular infection the drug is unreliable and saves only a relatively small proportion of animals.

2. The strain of Cl. welchii (type A) selected for test is not insusceptible to the action of sulphapyridine. A significant degree of protection against intradermal infection may be obtained however, only when a prophylactic dose of the drug is given. The drug is apparently without action against intramuscular infection with this strain.

3. Under the particular experimental conditions sulphanilamide is much less effective than sulphapyridine against infection with either V. septique or Cl. welchii.

4. There is no evidence that sulphapyridine given per os neutralizes the toxins of V. septique or Cl. welchii injected intravenously.

5. It is possible to control infection with V. septique by antitoxin or antibacterial serum given at a time when sulphapyridine is of little use. Cl. welchii antitoxin has a marked therapeutic effect in infection with this strain of the organism but sulphapyridine given only after infection is apparently without action on the course of the disease.

6. In intradermal infection with V. septique the combined action of sulpha-pyridine and antitoxin or of sulphapyridine and antibacterial serum effects a saving in life much greater than would be expected if a mere summation effect was in question. A similar effect was observed in intramuscular infection provided the administration of the drug was sufficiently prolonged. No such synergic effect is produced by the combined action of antitoxic and antibacterial serum.

7. In Cl. welchii infection the combined action of antitoxin and sulpha-pyridine produces a noticeable synergic effect but the evidence on this point is less clearly defined.

8. The pathogenesis of infection with spore-bearing anaerobes is discussed in relation to prophylaxis or therapy with chemotherapeutic agents, antitoxin, antibacterial serum and combinations of such.

9. The statistical aspect of summation effects is briefly considered pending a forthcoming mathematical analysis, by Dr K. Mather, of the figures obtained in experiments on synergic action.

1. The types of tubercle bacilli have been determined in the sputum of 515 cases of pulmonary tuberculosis occurring in the middle and south of Scotland.

2. Of the 515 cases 484 were human (476 eugonic and eight dysgonic) and thirty-one were bovine infections.

3. With the exception of the strains from one case (case 28) all the bovine strains, seventy in number, were typical culturally and fully virulent for rabbits.

4. The attenuated strains, two in number, from case 28 were slightly less virulent than typical bovine strains for rabbits and (one strain) for guinea-pigs.

5. The percentage of bovine infections found in this series, including the Cumberland case, during the years 1931–9 was 6·0, but excluding that case it was 5·8.

6. The percentage of bovine infections found by Munro during about the same period and covering the same regions was 5·0%.

7. In Munro's series strains of bovine tubercle bacilli were obtained from fifty-eight out of 1165 persons (5·0%). Five of his cases yielded attenuated bovine strains and in one of these the pulmonary tuberculosis was preceded by tuberculosis of the thoracic spine.

8. In my series the attenuated tubercle bacilli came from a case (case 28) of pulmonary tuberculosis which was preceded nearly 20 years previously by tuberculosis of the lower dorsal spine.

Dr Munro and others have made post-mortem examinations on cases of phthisis pulmonalis due to bovine bacilli, but I wish to defer reference to these until we can review them altogether.

In this series there are seven instances of cervical gland enlargement and one instance (case 28) of spinal tuberculosis occurring previous to the development of phthisis pulmonalis. These, I think, are examples of alimentary infection with the bovine tubercle bacillus. Thus, with the three autopsies previously mentioned, there are eleven cases, or about one-third, which are almost certainly alimentary in origin. As for the rest of the cases, 20 in number, no glandular enlargements in neck or abdomen were detected but the majority, if not all, were probably alimentary in origin, since all the persons drank a lot of raw milk and only five came into direct contact with cattle in their employment.