This was a very strong indication that the rods were the cause; the maternal and foetal blood are separated by a membrane through which fluids and substances in solution pass; but insoluble substances, even when very minutely subdivided, do not pass the membrane.

If the cause were a poison in solution, the foetal blood would have been as toxic as the maternal.

The blood of infected cattle was filtered through filters made of unbaked porcelain and having very fine pores which allowed only the blood fluid to pass, holding back both the blood corpuscles and the rods, and such filtered blood was found to be innocuous.

It was further shown that the rods increased enormously in number in the infected animal, for the blood contained them in great numbers when but a fraction of a drop was used for inoculation.

Attempts were also made with a greater or less degree of success to grow the rod shaped organisms or bacilli in various fluids, and the characteristic disease was produced by inoculating animals with these cultures; but it remained for Koch, 1878, who was at that time an obscure young country physician, to show the life history of the organism and to clear up the obscurity of the disease.