R. VANFURTH Infection is an inseparable part of communal life, and infections are more common and more severe in hospital communi ties because the sick are more easily infected than the healthy. However, even though progress in the medical sciences has meant that many more patients suftering from relatively severe diseases can be helped at present, the use of more sophisticated and complex treatment leads to impairment of the defence mechanisms in more patients than was the case ten to twenty years ago, and these patients are also more prone to develop an infection. Two questions are particularly relevant in this context. 1) Under what conditions do hospital infections occur? Defects of host defence mechanisms are of great importance in this respect. Such defects can be due to the disease or to the treatment given to the patient. 2) Which of the host defence mechanisms can be affected by a stay in the hospital? Among the factors involved in the host defence against infections (Table I), a number are especially important in this respect. For instance, venepuncture, indwelling catheters, and surgery all cause a breach in the surface structures. Anaesthesia causes temporary impairment of mechanical factors. Vascularization may be defective -- especial ly in the aged and patients with diabetes mellitus -- and this may complicate the healing of wounds in the skin and mucous membranes after surgery."

Recent reviews of respiratory-tract affections caused by M. pneumoniae under- score the benign and often subclinical course of the infection. Severe pneumonia with a reticular or acinar pattern is certainly unusual and a fatal outcome is rare, but the incidence of both is underestimated. Erythromycin and tetracyclines are the first-choice antibiotics. There is evidence indicating the importance of im- munopathogenic mechanism in provoking pneumonia and even respiratory failure. REFERENCES 1. Krech U, Price PC, Jung M: The laboratory diagnosis and epidemiology of mycoplasma pneumoniae in Switzerland. Infection 4:33, 1976. 2. Fischman RA, Marschall KE, Kislak JW: Adult respiratory distress syndrome caused by mycoplasma pneumoniae. Chest 74:471, 1978. 3. Reigner Ph, Domenighetti G, Feihl F, Bonjour JPh, Perret CI: Syndrome de detresse respiratoire aigu sur infection a mycoplasme. Sch Med W 110:220, 1980. 4. Kaufman JM, Cuvelier CA, Van der Straeten M: Mycoplasma pneumonia with fulminant evolution into diffuse interstitial fibrosis. Thorax 35:140, 1980. 5. Murray HW, Masur H, Senterfit L, Roberts R: The protean manifestations of mycoplasma pneumoniae infection in adults. Am J Med 58:229, 1975. 6. Levine DP, Lerner AM: The clinical spectrum of Mycoplasma pneumoniae infections. Med Clin N Am 62:961,1978. 7. Twomey JA, Espir ML: Neurological manifestations and Mycoplasma pneumoniae infection. BMJ 2:832, 1979. 8. Kingston JR, Chankock RM, Mufson MA, Hellman LP, James WD, Fox HH, Mankoma C, Boyers J: Eaton agent pneumonia. JAMA 176:118, 1961.

R. VANFURTH Infection is an inseparable part of communal life, and infections are more common and more severe in hospital communi ties because the sick are more easily infected than the healthy. However, even though progress in the medical sciences has meant that many more patients suftering from relatively severe diseases can be helped at present, the use of more sophisticated and complex treatment leads to impairment of the defence mechanisms in more patients than was the case ten to twenty years ago, and these patients are also more prone to develop an infection. Two questions are particularly relevant in this context. 1) Under what conditions do hospital infections occur? Defects of host defence mechanisms are of great importance in this respect. Such defects can be due to the disease or to the treatment given to the patient. 2) Which of the host defence mechanisms can be affected by a stay in the hospital? Among the factors involved in the host defence against infections (Table I), a number are especially important in this respect. For instance, venepuncture, indwelling catheters, and surgery all cause a breach in the surface structures. Anaesthesia causes temporary impairment of mechanical factors. Vascularization may be defective -- especial ly in the aged and patients with diabetes mellitus -- and this may complicate the healing of wounds in the skin and mucous membranes after surgery."

Mononuclear phagocytes, which include macrophages, monocytes and their precursor cells, are the most important cells in the host defence against micro-organisms and tumor cells. During the last twenty-five years research on the biology of mononuclear phagocytes has increased tremendously. This motivated Professor R. van Furth to organize five international conferences on this subject in Leiden, the Netherlands. The edited proceedings of these meethings were published: in 1970 Mononuclear Phagocytes; in 1975 Mononuclear Phagocytes in Immunity, Infections and Pathology; in 1980 Mononuclear Phagocytes -- Functional Aspects; and in 1985 Mononuclear Phagocytes -- Characteristics, Physiology and Function. Reviews of these volumes, published in international journals, praised them as the most up-to-date state of the art publications. The publication of 1991 includes 88 chapters written by more than 200 authors.