PRACTICAL CONDUCT OF EXERCISE IV 141 



Of further help for maintenance of the preparation's temperature is a warm bottle— the 

 six-sided half-litre glass bottle of chemical reagent purveyors answers well to place against 

 the side of the preparation or under pelvis when in prone position. This serves also as a 

 useful prop to support the trunk of the carcase in suitable positions. 



Failure of maintenance of the temperature during a class-period is, as experience shows, 

 usually due to the student's mistakes in using imperfectly warmed saline and in leaving 

 wound surfaces unduly exposed. As to respiration, the accident most likely to disturb the 

 preparation is blocking of the trachea or its cannula with mucus. Glass instead of metal for 

 the cannula has, besides greater cleanliness, the advantage of allowing the collecting of mucus 

 to be seen. A small feather passed through the cannula and twisted will relieve this, 

 bringing the mucus with it on withdrawal. 



The operation table's top stands 110 cm. from the floor, the upper limit of convenient 

 height for operating for students some of whom are women. For this height of table the 

 Brodie kymograph table is improved by shortening the legs by 7 cm. There is room on the 

 table for operating instruments, and for the indispensable litre-mug of warm Ringer-Locke 

 and soaked cotton-wool pledgets ; also for the bridge-key of the secondary circuit to be 

 clamped on table-edge when in use for stimulation. Gleets are not provided round the 

 table-edge ; they prove inconvenient rather than helpful for preparations such as those used 

 in this course, not requiring rigid fixation. An upper and lower shelf in the table frame 

 serve for inductorium, voltaic cell, &c. 



Obs. 12, 13. Prof. Noel Paton combines with the inspection of the heart the registration 

 of the movements of auricle and ventricle respectively, by, for instance, a pair of Brodie 

 class-demonstration heart-levers {Essentials of Experimental Physiology, T. G. Brodie, 

 London, 1898, p. 140). The graphic observation so obtainable makes an excellent exercise 

 readily performed by the student. It is not included in the exercise as arranged here 

 because the time it requires precludes the student's reaching some other points which by 

 restricting the procedure to inspection he can reach and are important for him early in his 

 course. It is to be remembered that the student, when once introduced to the graphic method, 

 tends to lean too exclusively on the written record even to the neglect of inspection of what 

 is happening in the living parts ad oculos before him. An early exercise wholly devoted to 

 observation by actual inspection has, therefore, its educational value. Should, however, the 

 time-limits permissible for the course allow the content of the exercise to be spread over 

 two consecutive class-meetings the auriculo-ventricular graphic has special value for that part 

 which deals with escape of ventricle under r. vagus inhibition. 



Obs. 14, 15. Circulation in the frog's web. For this observation ethylo-urethane in the 

 dose mentioned excellently replaces curare and has the advantages of greater invariability 

 of action and dosage and of its solution keeping without deterioration ; it interferes with the 

 heart's action much less than do many of the samples of curare now procurable. 



EXERCISE V 



The student's instructions for this exercise are given in considerable detail because two 

 of the items of technique, namely, kymographic registration of arterial pressure and 

 intravenous injection by the needle-syringe, are basal for many observations that 

 follow. 



