Deposition in the Respiratory Tract of Cattle of Spores of Bacillus subtilis var niger by Inhalation and by Nasal Instillation

Spores of Bacillus subtilis var niger were deposited in the lungs, tracheae and nasal cavities of four calves by aerosol inhalation and in three calves by intranasal instillation. From each calf 20 specimens of lung tissue, each weighing one gm, three of trachea and three of nasal mucosa were examined for spore content. The average numbers of spores per gm of lung tissue from animals exposed to aerosols were 3.05 and 4.84, 2.35 and 2.02 x 10⁴. Lungs from animals exposed intranasally contained only 747, 62 and 1424 spores per gm of tissue respectively. Animals exposed intranasally had a hundred to a thousand fold more spores on nasal mucosa than animals exposed by aerosol and the latter had a thousand fold more spores on tracheal mucosa than calves exposed intranasally. Aerosol inhalation exposed the lung and trachea more densely and uniformly than did intranasal instillation.