XXVI CHOICE OF METHODS 



An untidy laboratory is not a sign of industry but an indicator of carelessness, 

 and sometimes a source of actual danger to the occupants. 



9. To Detect Deviations from Normal 



The Normality of a tissue or organ is often in doubt. There is no single 

 technique capable of yielding an unqualified answer. Since some properties 

 may be normal while others are abnormal (pathological) we need first to be told 

 the property under consideration. If it is, for instance, the amount of contained 

 pigment, this can be said to be normal when it is the amount usually present in 

 a particular tissue under the same conditions. By the word "usually" is in- 

 tended in the majority of cases, that is in 51 per cent or in any higher percentage. 

 The phrase "same conditions" means that the conditions likely to influence the 

 amount of pigment are so nearly alike as to be not responsible for any difference 

 observed between the property of the tissue where normality is in question and 

 that of others of the same kind. Thus, we could say with reasonable assurance 

 that the amount of pigment is normal if it is that usually demonstrated by the 

 same technique in tissues of the same kind of animals of the same species, sex 

 and age living under the same conditions. Judgment is necessary in specifica- 

 tion of possibly modifying conditions which will depend to some extent on the 

 property under consideration and on the number of observations necessary to 

 establish the percentage within the limits of probability. It would not do to 

 compare the amount of pigment in the specimen, the normality of which is in 

 question, with that in too few others. This is the statistical definition of nor- 

 mality which is not universally accepted but which is useful and easily under- 

 stood. 



Only a few samples of the various kinds of technique have been mentioned in 

 this survey as a kind of menu from which to make a selection or to obtain clues 

 to other methods that may fit the case. Many of them are very ingenious and 

 were only discovered after wisely conceived attempts to overcome practical 

 difficulties. This overcoming of obstacles is a pleasant experience. It calls for 

 actual work and experiment and appeals to many of our best minds. The 

 techniques may be regarded as keys by which scientific treasure can be unlocked. 

 Unused they are worthless. 



