especially as the subject is one to which I have not given any personal 

 attention. The investigation of the second class, that of the correlation 

 of the activities of organs, has by reason of its greater obscurity, or of the 

 greater difficulty of its practical application in medicine, fallen largely 

 to the province of the physiologist, and I therefore propose to deal almost 

 exclusively with those members of this class of reactions which have so 

 far been definitely ascertained. 



Before, however, entering into details of any particular correlation, it 

 may be profitable to consider what we may expect to be the nature of 

 the substance which will, in any given case, act as a chemical nexus 

 between different organs. We are dealing here with a question of 

 general pharmacology. As Ehrlich has pointed out, the chemical sub- 

 stances which act on the body or parts of the body, producing physio- 

 logical or pharmacological effects, can be divided largely into two main 

 groups. Ehrlich's conception of the first group is bound up with his 

 conception of the nature of the living protoplasmic molecule as a living 

 nucleus with side chains of various descriptions. Assimilation of food- 

 stuffs consists in the linking on of the food molecule as a fresh side 

 chain to the central nucleus. The common feature among the substances 

 of the first class is their close resemblance to an assimilable substance or 

 foodstuff. All these substances acquire a close attachment to, or even 

 identification with, the living protoplasm, and as a rule their effects are 

 apparent only after sufficient time has elapsed for their building up into 

 the protoplasmic molecule. To this class belong the numerous bodies, 

 closely allied in their chemical character to the proteids, which are 

 designated as toxins. All are produced by the agency of living organisms. 

 I need only adduce as examples the various products of the pathogenic 

 bacteria, such as diphtheria and tetanus, the poisonous toxins of higher 

 plants, such as ricin and abrin, and those formed as a weapon of offence 

 by higher animals, such as the active principles of the various snake 

 venoms. According to Ehrlich, these all resemble assimilable foodstuffs 

 in that they possess a haptophore group, by which they can anchor them- 

 selves on to the living molecule, becoming thus part of its side chains. 

 The toxophore group thus introduced into the living molecule upsets 

 and disorganises its reactions, leading by disorder of one or more func- 

 tions to the death of the animal. In most cases the toxophore group 

 is specific for some definite tissue or type of cell. Thus tetanotoxin 

 exercises its effect almost entirely on the peripheral sensory neurones. It 

 is doubtful, however, whether the haptophore group is so specific, if we 

 are to accept Ehrlich's conception of the mode of formation of antitoxins ; 

 since we may get formation of antitoxins in animals where the toxic 

 effect is entirely wanting. 



The idea that these toxins ape the part in the protoplasmic mole- 

 cule of an assimilable foodstuff does not involve as a necessary sequence 

 the formation of antitoxins or antibodies to the normal foodstuffs. That 

 the power of assimilation is independent of the power to produce 

 antibodies has been shown by van Dungern in a research specially 



