THE ACTIVITY OF THE HORMONES 13 



for instance, that an increased amount of albumin in the cir- 

 culation, by its direct influence upon the organs, gives rise to 

 an increased decomposition of albumin. Thus, albumin in the 

 form in which it is produced by the digestive apparatus, is both 

 a nutrient and a hormone. Another nutrient which acts likewise 

 as a hormone, is the oxygen inhaled by the lungs, though its 

 production is not the result of any organic activity. 



In spite of this dual function it is, in many instances, not 

 only possible but expedient to draw a distinguishing line between 

 the nutrient secretions and the hormones. The factor of dif- 

 ferentiation is to be found in the quantitative conditions. Sub- 

 stances which supply either material or energy, or both, must 

 inevitably be present in considerable quantities. Hormones, on 

 the other hand, which give rise to energetic processes, or influence 

 them in a special direction, must be able to produce their effect 

 even in minimal quantities. The practical outcome is this; that, 

 where a nutrient secretion is lacking it is useless to attempt 

 artificial substitution, because of the large amount of material 

 which would be required ; whereas we are frequently able artifi- 

 cially to replace a missing hormone. 



The true hormones have been variously classified according 

 to the manner in which they act. Thus we have formative and 

 protective, growth-promoting and growth-retarding, stimulant and 

 inhibitory. 



If we adopt Hering's theories upon the chemical processes 

 in living matter as a basis for classification, the hormones will 

 fall into two groups ; according to the nature of their activity 

 they are either assimilatory or disassimilatory. Those in the first 

 group promote the anabolic phase of metabolism those processes, 

 that is, which conduce to the building up of living matter. Those 

 in the second promote the katabolic phase, for they favour and 

 promote the decomposition of living matter. Each stimulus to 

 assimilation necessitates an inhibition of disassimilation, and 

 vice versa. 



All the known hormones can be included in one of these two 

 classes. The promotion of growth supplies an example of an 

 assimilatory hormone which, at the same time, exerts an inhibitory 

 influence upon disassimilation. In the case of retardation of 

 growth the process is reversed. Every increase in normal activity, 

 whether this be an improved secretion, a stronger muscular action, 

 or any other augmented performance, is always associated with 

 an increased disassimilation, which is the work of a dis- 

 assimilatory hormone. But it must be remembered that, in the 

 organism, as elsewhere, no work can be performed without ex- 

 penditure. So long as the metabolic equilibrium is maintained, 

 every decomposition must be inevitably succeeded by a regenera- 

 tion. Even in the case of hyperactivity, so long as exhaustion 

 does not supervene, there will be a continual regeneration of the 



