328 PRINCIPLES OF GENERAL PHYSIOLOGY 



SPECIFICITY 



We are quite justified in speaking of the relation between the u- and (3 gluco- 

 sides and maltose and emulsin as a "specific" one, although the difference 

 may be merely quantitative, as we shall see presently. There are, however, 

 many degrees of specificity ; emulsin acts on a great variety of glucosides, trypsin 

 on all proteins, while invertase is said to have no action on any substance but 

 ( am- sugar. This last fact places a difficulty in the way of accepting Bertrand's 

 hypothesis, at least in its simplest form. Since, if invertase merely activates 

 acid, it should be capable of hydrolysing maltose and lactose as well as saccharose. 



But it seems to me that the practice of some investigators in assuming a 

 separate enzyme for every substrate acted upon is not warranted by the facts. 

 When we say that there is a salicinase in what is usually called emulsin, if we 

 mean anything more than that emulsin hydrolyses salicin, we are going beyond 

 what is justified by the experimental evidence. It is true that, under some 

 conditions, extracts containing emulsin may act more powerfully on salicin than 

 upon some other glucoside, while other extracts may act better on the latter ; but 

 it has not been shown that this is due to anything other than different conditions. 

 It is to be remembered that even acid will hydrolyse some glucosides much more 

 readily than others. Until a separate enzyme is prepared which acts on no other 

 substrate but salicin, under any conditions, the name salicinase should not be 

 used. At the present time it would be more profitable to devote attention to the 

 various ways in which the rate of action of an enzyme on various substrates can 

 be modified by change of conditions. 



The multiplication of names may even be mischievous in leading to the belief 

 that new knowledge has been obtained when a phenomenon is described by a 

 name derived from a classical tongue instead of in English. 



There is risk, for example, that when we say that the injection of a foreign protein causes 

 the production of a "precipitin" for the protein, we may imagine that this "precipitin" has 

 been shown to be a definite chemical individual, instead of a mere description of the fact that 

 a precipitate is formed. The "side-chain theory" of Ehrlich, great as has l>een its use in 

 suggesting problems for investigation, is, at present, overburdened with multitudes of names, 

 which consist, for the most part, merely of descriptions of the phenomena, although they 

 suggest actual substances. There are many signs that one or two simple explanations, on 

 the basis of colloidal chemistry, will be found to put an end to most of these names. 



One is tempted, indeed, to make a well-known quotation from Moliere (1673). 

 The reader will remember that in the ballet of " Le Malade Imaginaire," which 

 ballet is a satire on medical examinations, one of the medical students sings 

 (tome v. p. 308 of Hachette's edition) : 



" Mihi a docto doctore 

 Domandatur causam et rationem quare 

 Opium facit dormire. 

 A quoi respondeo, 

 Quia est in eo 

 Virtus dormitiva, 

 Cujus est natura 

 Sensus assoupiie." 

 Which I may venture to translate thus : 



"The learned doctor asks me 

 The cause and reason why 

 Opium sends to sleep. 

 To him I make reply, 

 Because there is in it 

 A virtue dormitive, 

 The nature of which is 

 The senses to allay." 



For this profound answer the candidate receives his diploma with acclamation, 

 together with his licence to "kill and to cure." 



Incidentally, I would call attention to the fact that this play was the last written by its 

 author, although it is regarded by many as his best work. This fact may be commended to 



