be hereditary. It must be admitted that there are different 

 types of physiological constitutions manifested among 

 various healthy individuals ; yet so elastic and indefinite are 

 the characters by which these are distinguished, that every 

 degree and variety of transitional forms are frequently 

 manifested. In the same way, no hard and fast line of 

 demarcation can be laid down as dividing purely physiological 

 from pathological conditions, and as even health itself is an 

 arbitrary relative condition, so physiological phenomena 

 merge imperceptibly into those which are pathological. In 

 this group of constitutional disorders " the stability of the 

 dynamic equilibrium of the vital processes is different from 

 that which subsists in health depends immediately upon 

 the morbid change which the vital processes have undergone 

 in regard to their force and direction, and is, therefore, 

 ultimately bound up with the very essence of every constitu- 

 tional disorder." It is quite possible that an individual 

 suffering from one or other of these nutritive disorders may 

 for a long time appear in excellent health, until, in fact, 

 some critical epoch, or external influence, or some inter- 

 current malady will develop the morbid tendency into a 

 well-marked pathological condition. In the production of 

 these, as in that of other, diseases or disorders, two sets of 

 causes are usually recognised viz., external or exciting, and 

 internal or predisposing. Of the former we must be careful 

 to exclude, in general terms, those of an infective or toxic 

 character, from those denominated " autogenetic," which 

 may be said to consist in some deficiency, unsuitableness, 

 or excess of the normal vital stimuli, as light, air, warmth, 

 food, exercise, etc. 1 Of the internal or predisposing causes, 

 which influence the development of the general disorders of 

 1 Immermann. 



