The work of Dr Zaidi on experimental silicosis has shown that in spite of the same chemical nature, the various forms of free silica differ in their fibrogenic action and that the optimum particle size of silica dust to cause maximum damage to the lung is in 1-2 m diameter range. Dr Zaidi experimentally established the pathogenesis and etiology of progressive massive fibrosis of the coal workers, lungs. He has established that the combined action of Tubercle bacilli and coal-mine dust produces an extensive pulmonary disease.