DEVELOPMENTAL MECHANICS. i8l 



To sum up the results of observation in the pathology of the 

 higher vertebrates, we may say that pathology is essentially the 

 doctrine of phenomena which are in themselves normal, but 

 which manifest themselves in the wrong place, at the wrong 

 time, or in the wrong magnitude or direction ; for all pathologi- 

 cal processes, a few kinds of decay (like amyloid and waxy 

 degeneration) excepted, also occur as normal phenomena. 



Hence there do not occur in the pathological conditions of 

 these animals any modi operandi which are foreign to normal 

 development or any new substantive or even prodttctively forma- 

 tive modi operandi ; and hence in case of secondary changes 

 pathology has only to investigate the way in which the organ- 

 ism makes use of its normal modes of formation and reaction 

 during or after disturbances of the normal conditions. 



Of course these results of pathology hold good also of arti- 

 ficial experiments. We are able to conclude, therefore, from 

 the reactions which take place after experimental or pathologi- 

 cal changes as to the modi operandi which also occur under nor- 

 mal conditions, but which operate normally with different inten- 

 sity and at a different time. 



On the other hand, whenever regeneration of destroyed 

 parts occurs, the mechanisms of indirect development are put 

 into activity. These were referred to above. 



Here we are concerned with the secondary changes of other 

 parts, which following upon primary disturbance are either 

 themselves disturbances ; in this case they indicate that the 

 primarily affected part is necessary to the maintenance or 

 development of the secondarily affected part, and hence in 

 some way participates in its production, thus exercising a 

 " trophic " influence upon it. 1 



Such conditions follow from the secondary atrophy of the 

 sensory or motor nuclei of the brain and spinal cord when their 

 respective peripheral end-organs are removed soon after birth, 

 and inversely from the aplasia of the muscles after destruction 

 of the motor ganglion cells of the anterior cornua in infantile 

 paralysis ; from the degeneration of the nerves when they are 

 separated from their respective ganglion cells, etc. 



1 There is only one alternative mentioned in this sentence, the other clause 

 having been omitted. W. M. W. 



