304 THE CAUSATION OF DISEASE. 



may almost certainly conclude that there is no abnormality ; 

 and the same may, perhaps, be said of most of the glands. I 

 suppose, for instance, that, given a perfectly healthy liver, a 

 skilled observer could with certainty pronounce it to be such. 



A second test remains to us — viz., functional efficiency. This, 

 as we saw in the last chapter, is the great criterion of 

 normality. We ask ourselves : Do the tissues carry on their 

 functions properly ? But if we wish to obtain a criterion of 

 normality for S it is obvious that we must qualify the question, 

 seeing that individuals differ in respect to different E's. We 

 must ask : Do the tissues carry on their functions properly 

 when the body is subjected to a standard normal E ? We 

 saw, however, that it is no easy matter to determine such a 

 standard ; that in endeavouring to erect a standard E, the only 

 plan open to us is to exclude all those forms of E to which 

 different individuals respond very differently, such as the 

 ague poison and extremes of temperature, and to include the 

 bare essentials to life, such as food, air, certain temperature, 

 and exercise. Given such a standard environment, the 

 functional test may be expressed as follows : — If the tissues of 

 the body do not carry on their functions properly under this 

 standard E, there must be distinct abnormcdity of structure.* 



These two methods — i.e., the method of direct examination 

 of the tissues, and that founded on the observation of functional 

 efficiency — together afford the most perfect test of structural 

 abnormality at our disposal. 



But although this double method is the most perfect of 

 which the circumstances of the case allow, it has its imperfec- 

 tions. As regards the method by examination, it is for the 

 most part available only after death, and even then an ab- 

 normality of tissue may escape our most diligent search. And 

 as regards the observation of functional efficiency, it, on the 

 other hand, is obviously one that can only be applied during life, 

 when it is no easy matter, as we saw in the last chapter, to be 

 absolutely certain that the functions of an organ are going on 

 perfectly; as a matter of fact, the most serious structural 

 disease may, quite unknown to us, lurk in an individual, for 



* These remarks are subject to the qualifications contained in the last 

 chapter. 



