Page:The Harveian oration 1888.djvu/35

27 itself at once in the tissue into which it has penetrated, and grows on in and with the growing plant, and produces the disease. The germ-tubes of Cystopus may indeed make their way for a short distance into all the other parts of the plant, but are unable to establish themselves inside it and continue their development. The plant is for the future safe from the attacks of the parasite as soon as the cotyledons have fallen off. The two or the twenty rusted plants in the bed are the ones in which the fungus attacked the cotyledons in good time; if it had attacked the thousand others in equally good time, all would have been rusted. They continued healthy, because they were not infected in the stage in which they were open to infection, that is, predisposed."

We may take another example from the human subject. Ringworm of the scalp due to the fungus Tricophyton tonsurans is not infrequently seen in children under 16 years of age, but after that age, though the fungus may affect other parts of the body, the scalp is generally free from it. Some change has taken place in the tissue there, which makes it less suitable for the growth of the parasite.

Now may not the function of the glands to which I have just now alluded, viz. that of destroying or neutralising effete or toxic products formed in the system, have some bearing upon the development of tuberculosis.] Thirty years ago it was suggested by Buhl that in the human subject acute miliary tuberculosis was due to the absorption into the blood of caseous matters from various sources. "It afterwards became the fashion to regard tubercle as always a secondary product the origin of which was sought for in 'caseous foci' of which the formation was supposed to precede, in all cases, the development of tuberculous lesions. . . The acute