PHYSICAL METHODS IN PHYSIOLOGY 89 



physical nature may completely alter its effect. The study of 

 immunity also — a matter of the most profound practical import- 

 ance and of the greatest theoretical interest and significance — 

 continues to lack any really satisfactory chemical or physical 

 principles to explain, or to correlate, the very complex series 

 of reactions undoubtedly occurring in the chemical interplay 

 between the invading organism, the body fluids, and the body 

 cell. The facts of pharmacology, of biochemistry, and of im- 

 munology all suggest the existence of substances with a highly 

 specific chemical structure, fitting into some portion of the 

 chemical machinery of the living cell in the same way as a key 

 fits into a lock or a bolt fits into a nut : but our knowledge of 

 the chemical structure of the living cell, as distinguished from 

 that of the products of its activity, disintegration, or destruction, 

 is still so imperfect that we have at present no sure evidence as 

 to the nature of the reactions in which chemical " messengers," 

 drugs, vitamines, or the various factors in immunity, play 

 their diverse parts. The most hopeful method, at present 

 available, of investigating the chemical structure of the living 

 cell itself lies perhaps in employing the highly specific nature of 

 the reactions associated with anaphylactic shock, on the lines 

 of the suggestive and beautiful work of Dale and his colleagues. 

 The attempt, in any case, to advance by chemical methods, 

 even though only partially successful, has at any rate made 

 us realise the necessity of further knowledge of the internal 

 chemical machinery of the cell, and of the organisation and 

 distribution of that machinery, and, since to realise the existence 

 of a problem is to go half-way to solving it, while to state it 

 in precise terms is to go still further, we may look forward 

 hopefully to the day when the problems of biochemistry, of 

 pharmacology, and of immunity will be susceptible of at least 

 as exact a treatment as is being applied now to the elucidation 

 of the structure of the crystal or the atom. That day may be 

 distant, but when it dawns it will give mankind a tool surpassing 

 all the dreams of the alchemist. 



