  Jeans showed analytically that, in an infinite uniform-density isothermal
gas, plane-wave perturbations collapse to dense sheets if their wavelength,
$\lambda$, satisfies $\lambda > \lambda_{_{\rm JEANS}} = (\pi a^2 / G
\rho_{_0})^{1/2}$ (where $a$ is the isothermal sound speed and $\rho_{_0}$ is
the unperturbed density); in contrast, perturbations with smaller $\lambda$
oscillate about the uniform density state. Here we show that Smoothed Particle
Hydrodynamics reproduces these results well, even when the diameters of the SPH
particles are twice the wavelength of the perturbation. Our simulations are
performed in 3-D with initially settled (i.e. non-crystalline) distributions of
particles. Therefore there exists the seed noise for artificial fragmentation,
but it does not occur. We conclude that, although there may be -- as with any
numerical scheme -- `skeletons in the SPH cupboard', a propensity to fragment
artificially is evidently not one of them.
