In principle, an unknown date of infection can be estimated from individual response times, provided some function of these with suitable origin is symmetrically distributed. Observed times are always skewly distributed, and either logarithm or reciprocal of time can be used to produce symmetry. Either is equally justifiable but the resulting estimates are not only very imprecise but are also inconsistent, so that neither is of practical value.

This paper describes the study of a mutant of Vibrio cholerae which is shown to be attenuated by its avirulence to mouse, rabbit and chick embryo. This mutant character is stable, and the avirulence of this strain probably results from its inability to multiply actively in the tissues of the infected animals. The need for the study of such attenuated strains as live vaccines in man is discussed, and certain aspects of immunity to cholera are reviewed.

The literature of human infection with Salmonella choleraesuis in China was fully reviewed with special reference to those written in Chinese language which are inaccessible to many readers. Compared with other regions of the world the ratio of S. choleraesuis to other salmonella infection in Hong Kong is high and is parallel to that in China. Dietetic habits of the local population apparently contribute to the high incidence. The clinical manifestations of 47 cases were outlined and details of the biochemical reactions and in vitro drug sensitivities of these strains were described. Two diphasic H2S-positive strains were encountered.

An investigation into the antibiotic sensitivity of B. abortus biotypes to polymyxin B sulphate, amphotericin B, and bacitracin has shown that the dye-sensitive strains are also antibiotic-sensitive; and preliminary experiments suggest that these two properties are not genetically related.

The results suggest that biotype 2 can be subdivided on the basis of antibiotic sensitivity pattern, and that this could be of epidemiological significance.

Investigation into the antibiotic sensitivity pattern of the dye-sensitive variant B. abortus, biotype 4, leads us to believe that this strain should be reclassified as a separate biotype and provisionally called biotype 10.

1. The strain HFEM of herpes simplex virus is highly virulent for the 5-week-old mouse when inoculated intracerebrally; the LD50 and the ID50 both being close to the egg infectious unit. It is also virulent when given intraspinally.

2. When inoculated peripherally it seldom causes nervous symptoms in the normal mouse but regularly does so if inoculated into skin which has previously been given a subcutaneous injection of 10% sodium chloride.

3. After intradermal inoculation of pretreated mice with strain HFEM, the paralysis is preceded by the appearance of infective virus in the blood, the sciatic nerve and the central nervous system. Invasion of the central nervous system is prevented by interruption of the local peripheral nerve.

4. There is no evidence that virus enters the central nervous system by way of the lymphatics or by direct extension through the tissues.

5. After intravenous inoculation virus does not invade the central nervous system unless (a) massive inocula are used or (b) the brain is traumatized by injecting sterile saline. After peripheral inoculation insufficient virus to infect even traumatized brain seems to circulate in the cerebral vessels. Paralysis and invasion of the central nervous system are not prevented by circulating neutralizing antibody given 18 hours after inoculation.

It therefore appears that invasion of the central nervous system takes place only by way of the peripheral nerve.

Observations on the bacteriological contamination of the air have been made in an operating room fitted with three alternative systems of ventilation.

These were; A, downward displacement ‘piston’; B, moderate velocity turbulent; C, low velocity turbulent.

The volume of the ventilating air supplied was the only characteristic of the ventilation which affected the contamination levels reached during operations. No significant differences could be detected between the three ventilating systems in this respect.

Unavoidable temperature differences in the operating room render it generally impossible to produce effective downward displacement air movement with ventilating air supplies which do not exceed 1500 ft.3 per minute over a ceiling area of 300 ft.2.

Great differences were observed between the several carriers of Staphylococcus aureus in the extent to which they dispersed this organism into the air when working in the operating room.

The air of a subdivided surgical ward was sampled by the exposure of culture plates for 12 hr. periods 5 days a week.

A number of ‘broadcasts’ of airborne Staphylococcus aureus were observed; many of these were of very short duration. A single person could be recognized as responsible for 22 of the 33 broadcasts; in all cases dispersal seemed to be from carrier sites rather than from infected lesions.

There was little spread of the staphylococci between the 4 rooms of the ward. The frequency of nasal carriage of tetracycline-resistant S. aureus increased from 6·2% in patients examined during their 1st week to 13·2% in those examined in their 4th week in the ward; the rate for all S. aureus declined from 31·3 to 26·4%.

It is suggested that the long-period exposure of culture plates for the collection of airborne staphylococci may be useful in monitoring some aspects of hospital hygiene.

An outbreak of infection in a Premature Baby Unit due to a single strain of Pseudomonas aeruginosa is described. The outbreak lasted for 16 months, during which this organism was isolated from the faeces of 99/418 premature babies, many of them being symptomless carriers. There were seven deaths due to the infection. The source of the epidemic was not found. The main reservoir of infection was the babies' faeces. Though many full-term babies were symptomless carriers of the epidemic strain of Ps. aeruginosa, they were not ill.

Measures for control of the outbreak, and the aetiology of neonatal intestinal infection with Ps. aeruginosa are discussed.

Eighteen patients treated by tracheostomy and mechanical ventilation were studied in an attempt to determine whether contaminated ventilators could act as a source of Pseudomonas aeruginosa isolated from the respiratory tract. Twelve became infected. In seven instances it was possible to demonstrate prior contamination of the ventilator. Furthermore, eight of the patients had indistinguishable organisms on the basis of pyocine and phage typing, and six of the ventilators harboured the same organisms. The most likely explanation is cross-infection via contaminated machines.

A technique is described for the routine isolation of salmonellas from meat and bone meal samples used in animal feedingstuffs. The technique more than doubled the number of positives obtained by an orthodox method. Identical samples were used in the trial.

Two field trials of A 2 live influenza vaccine (Iksha) are described; the clinical reactions and antibody response in three earlier trials are compared.

The antibody response in the last two trials was unsatisfactory and was inferior to that observed in the earlier investigations. This reduction in response was probably due to an alteration in the virus during further passage.

Two pools of living influenza vaccine derived from the Russian A 2 strain Iksha had given discrepant results in clinical trials. The less effective pool showed an increased thermostability of haemagglutinin, an increased elution rate from red blood cells and a reduced ability to grow in chorioallantoic membranes at temperatures above 40° C. The relationship of these findings to the virulence of influenza viruses is discussed.