NATURE OF DISEASE. 127 



and passing new amoebae into each new daughter- 

 cell of the host. Here the processes of stimula- 

 tion, hypertrophy and further division are repeated, 

 until hundreds or thousands of the turnip 

 root-cells are infected. The externally visible 

 result is the formation of distorted swellings on the 

 root (Finger and Toe), most of the cells of which 

 are abnormally large and filled with amoeboid 

 Plasmodiophora protoplasm, which finally devours 

 the turnip-protoplasm and itself passes over into 

 spores. Here we have most convincing proof of 

 the stimulation of protoplasm by other protoplasm 

 in direct contact with it ; and that the metabolism 

 of the host-cells is profoundly altered is shown 

 not only by the abnormal growth of the cells, but 

 also by the starvation of the rest of the turnip 

 plant as the Plasmodiophora gets the upper hand. 

 We have here, in fact, a local intracellular parasitic 

 disease, gradually invading large tracts of tissue 

 and eventually inducing general disease resulting 

 in death a state of affairs reminding us of cancer 

 in animals. 



Irritation and hypertrophy of cells, however, may 

 be induced by parasites which never bring their 

 protoplasm into direct contact with that of the host. 

 Many Chytridiaceae penetrate the cells of plants, 

 and grow inside them as short tubes, vesicles, etc., 

 the protoplasm of which is separated by their own 

 cell-walls from that of the host-cell ; neverthe- 

 less hypertrophy and abnormal cell-divisions and 

 secretions are induced, and the effect even extends 

 to neighbouring cells e.g. Synchytriuvi showing 



