26 IXTRODUCTIOX 



ciples with which the student is unfamiliar. It often oc- 

 curs, however, that as the student gains in experience and 

 in technical ability, drags which have already been studied 

 may be reintroduced either as a matter of review, or to 

 demonstrate certain actions of other drugs which are not 

 evident until brought to light by the changed response of 

 certain structures to drugs injected secondarily, or to serve 

 as a check on the action of the apparatus and the general 

 teclmic employed in the experiment. For this latter pur- 

 pose great use is made of adrenaline in these experiments. 

 This often serves the double purpose of reviving an animal 

 when it is in a very feeble condition, and also gives the 

 student (aud hixtnictor) an immediate indication of the 

 accurary of the working of his apparatus and of the condi- 

 tion of the animal. It should be especially emphasized that 

 the extensive use made of adrenaline in many of the ex- 

 periments is solely for the purposes here indicated, and its 

 frequent injection should not be considered in any sense as 

 a useless repetition of the same experiment. 



It is imperative to use the strictest economy with the ex- 

 perimental material. For this reason it is desirable for 

 the students to learn everything possible from each animal 

 used. Consequently many experiments are listed here in 

 which a variety of reactions may be recorded at the same 

 time. The instructor should use his judgment in the case 

 of each group of students regarding the number of records 

 which the group will probably be able to successfully se- 

 cure. And he should not hesitate to eliminate any indicated 

 part of the experiment in which he believes the group will 

 fail. The author has, however, often been amazed at the 

 excellent success which students with some experience may 

 frequently obtain in carrying out exceedingly difficult and 

 involved experiments. And the writer recommends that 

 the instructor should not hesitate to permit a group of 

 students to attempt to carry out a difficult experiment 

 whenever he can advisedly do so. For it should be espe- 

 cially emphasized that a student's own failure may be of 



