was recovered from 13 of 28 calves with cuffing pneumonia and mycoplasmas were seen by electronmicroscopical examination of lung tissue from 10 of the 13 animals. Mycoplasmas were detected by electronmicroscopical examination of lung tissue from five of 11 calves that yielded mycoplasmas other than on culture. Mycoplasmas were detected in one calf with pneumonia from which organisms could not be cultured. These results indicated a significant association between the isolation of and the detection of mycoplasmas by electronmicroscopy.

Pulmonary tissue from six additional pneumonic calves with cuffing pneumonia was fixed and stained by the ruthenium red technique. was cultured from three of these calves and electronmicroscopical examination of pulmonary tissue from them demonstrated mycoplasmas with an extracellular capsule similar to that seen in pure cultures of These organisms were neither seen nor isolated from the pulmonary tissue of the other three calves.

The mycoplasmas were seen in close contact with the bronchial epithelium but never intracellularly. The cellular changes seen in the bronchial epithelium of the pneumonic calves were loss of cilia and protrusions of the apical cytoplasm of epithelial cells into the bronchial lumen; intracytoplasmic changes consisted of distension and disruption of the mitochondria and vacuole formations in the cytoplasm of the cells of the bronchial epithelium.


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