neutralise its physiological effects. It might be suggested that, in the 

 case of these chemical messengers, the formation of an antibody was a 

 local one and limited to the organ affected and that, in fact, their physio- 

 logical effect e.g., secretion was actually a pouring out of the antibody 

 to the chemical messenger. But, as we shall see later, experimental 

 evidence is entirely against this view, which, moreover, is not supported 

 by any known instance of a similar localisation of antibody as a result of 

 injection into the organism of any of the substances which belong 

 definitely to the toxin class. The formation of antibodies appears 

 to be, not a process of value in the normal physiological life of the 

 organism, but one which has been evolved as a chemical means of defence 

 to prevent the spread of injurious substances from the spot originally 

 affected or attacked. 



We are therefore forced to the conclusion that, if the processes of 

 coordination of activities among the organs of the body are carried out 

 under physiological conditions to any large extent by chemical means 

 i.e., by the despatch of chemical messengers along the blood stream 

 these emissary substances must belong to Ehrlich's second order of sub- 

 stances acting on the body and must fall into the same category as 

 the drugs of our Pharmacopoeia. Among these, indeed, specificity is 

 not wanting and is the basis of their classification by pharmacologists. 

 Thus we have drugs elevating or depressing the activity of the nervous 

 system ; we can excite secretion in all the glands of the body by pilocarpin ; 

 we can stimulate and finally paralyse the prseganglionic nerve endings of 

 the sympathetic system by the injection of nicotine, or arouse the ana- 

 bolic mechanism of the heart by the administration of digitalis. In all 

 these cases we are certainly interfering with normal processes. The 

 methods however, which we employ, are not at variance with those made 

 use of by the body itself in securing the harmonious cooperation of its 

 various parts. 



In discussing the internal chemical reactions of the body, it will be 

 convenient to divide them into two classes viz., those which involve 

 (i) increased activity of an organ, and (2) increased growth of a tissue or 

 organ. In both cases we must assume that the reaction to the chemical 

 stimulus is itself chemical, the first class including those changes 

 which are chiefly katabolic or dissimilative and are always associated 

 with activity, and the second class involving diminished katabolism and 

 increased building up or anabolism. We might, in fact, speak of the two 

 classes of chemical stimulants as augmentor and inhibitor. 



REACTIONS INVOLVING INCREASED ACTIVITY- OF ORGANS. 



The most striking, because the simplest, of this class of reactions is 

 that which determines in higher animals the adequate supply of a con- 

 tracting muscle with oxygen and the removal of its chief waste product, 

 carbon dioxide. The increased depth and frequency of respiration con- 

 tingent on muscular exertion are familiar to everyone, and we know that 



