High dispersion spectrograms of the Swan bands of diatomic carbon are obtained from samples enriched to 50 percent and 40 percent, respectively, in ${\mathrm{C}}^{13}$ and ${\mathrm{C}}^{14}$. The method of exciting an intense spectrum with microgram samples is described. To permit measurements of the alternating-intensity ratio, current densities in the source had to be limited so that the $\ensuremath{\Lambda}$-type doublets were well resolved. For ${\mathrm{C}}^{13}$, photometric measurements of this ratio give 3:1, showing that the nuclear spin $I=\frac{1}{2}$. The antisymmetric rotational levels have the higher statistical weight (Fermi-Dirac statistics). For ${\mathrm{C}}^{14}$, only the lines from symmetric levels appear. This shows clearly that $I=0$ for ${\mathrm{C}}^{14}$, and that the nucleus obeys Einstein-Bose statistics. Wave numbers are given of lines in the $R$ branches of the 0,0 band in the range $K=12 \mathrm{to} 20$, due to all molecular species containing ${\mathrm{C}}^{12}$, ${\mathrm{C}}^{13}$ and ${\mathrm{C}}^{14}$. An isotope effect in the splittings of the electronic triplets is investigated, and found to agree with that calculated from the general term formula for $^{3}\ensuremath{\Pi}$ states.