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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 de- 

 velopment. 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 in- 

 fected 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 develop- 

 ment 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 



