The new organism can, however, quickly become diseased and, by the transference of disease to it and by either parent, there is the appearance of hereditary transmission of disease, though in reality it is not such.

The ovum itself can become the site of infection; this, which was first discovered by Pasteur in the eggs of silkworms, takes place not infrequently in the infection of insects with protozoa.

In Texas fever the ticks which transmit the disease, after filling with the infected blood, drop off and lay eggs which contain the parasites, and the disease is propagated by the young ticks in whom the parasites have multiplied.

The same thing is true in regard to the African relapsing or tick fever, which is also transferred by a tick.

In the white diarrhoea of chickens the eggs become infected before they are laid and the young chick is infected before it emerges from the shell.