242 EXPEllIMENTAL INVESTIGATION OF THE ACTION OF MEDICINES. 



sometimes we may very conveniently use tliem both, as in the 

 case of protoplasm, the physical basis of life. 



Caution. — As I intend not only to describe the ways in 

 which experiments on the action of medicines are to be per- 

 formed, but also to give examples of the conclusions drawn by 

 various observers from the experiments which they have made, 

 and of the Vv'ay in which these conclusions have been applied, I 

 take this opportunity of strongly warning you, once for all, that 

 you must distinguish very carefully between the observations 

 actually made by any one and the conclusions which he draws 

 from them. Observations on the ehect of a drug may be 

 correct, and yet the theory of its mode of action be erroneous ; 

 and both of these may be right, and still the proposed applica- 

 tion of it to a disease may be valueless from ignorance of its 

 real pathology. All observations, too, are not to be taken as 

 facts : they must be confirmed by frequent repetition either by 

 the first observer himself or by others before they can lay claim 

 to this title. Their value depends to a great extent on the 

 observer, and is in proportion to his power of seeing correctly 

 what is before him, and the exactness of his description of what 

 he has seen. Perhaps erroneous statements are due in great 

 measure to the results of experiments not being noted at the 

 time when they were done, but written down from memory 

 some time afterwards. When this is the case, they lose in a 

 great measure their claim to the name of observations, and they 

 become merely thoughts or ideas of the observer. All experi- 

 ments should be noted down at the time when they are performed ; 

 and if they are not, the time which elapsed before they were 

 written should be stated, that future workers may know what 

 value to attach to the observation, and not be put to the 

 unnecessary trouble of disproving it if it be erroneous. Before 

 beginning an investigation, it is convenient to write out the 

 questions which we propose to ourselves, and to note down 

 what experiments will be necessary to answer them. We are 

 thus less likely to make experiments at random, and to waste 

 time without coming to any certain conclusion. 



Action on Protoplasm. — We may study the action of drugs on 

 protoplasm either in unicellular organisms like the Infusoria, in 



