Some effects of removing increasing proportions of the left caecum on the remaining caecal tissue and on the right caecum were studied in young chicks during a period of 35 d. The chicks were 22 d old when the operations were carried out. 2. No differences were detected between the gains in weight of the control and experimental groups of birds. 3. A marked negative linear relationship was observed between the dry weight of the amount of caecal tissue removed when the birds were 22 d old and weight of the left caecum at the end of the experiment. 4. The average growth rate of the left caecum (g dry tissue/week) was found to be dependent on the estimated weight of caecal tissue remaining after surgery. 5. No evidence was obtained to indicate that the growth of the right caecum responded to the removal of the left caecal tissue. 6. The morphology and histology of the operated caeca were found to be similar to the equivalent regions of the unoperated caeca. Surgical interference was not followed by any major changes in mucosal architecture. 7. In birds which had experienced unilateral caecectomy, the discharge of caecal faeces usually stopped for about 2 d. When caecal defaecation was resumed, the pattern of defaecation appeared to be the same as that observed in sham-operated birds with both caeca intact.
