PEACTICAL CONDUCT OF EXERCISE XII 161 



time of decerebration and then released as soon as danger of haemorrhage has passed. If 

 the circulation in the submaxillary region is stopped permanently the salivary secretion is 

 not obtainable. 



The student's operation is here described in a form suitable for one without previous 

 acquaintance with the region involved or with the manipulation of smaUish gland-ducts. 

 After having performed the experiment once the student will find he can curtail his incisions ; 

 thus he can do without an anterior transverse incision, the longitudinal incision can stop 1 cm. 

 in front of hyoid, and he can make the lengthwise skin incision 1 cm. to right of median 

 line ; the whole wound is thus smaller and the structures are less exposed to cooling. 



A difficulty is the relatively small size of the ducts. The more median, the sub- 

 maxillary proper, is usually slightly the larger. It does not matter for this exercise which 

 of them be chosen, the submaxillary or the retrolingual ; the corda tympani is secretory to 

 both the glands. The capillary-ended cannula need not be tied in ; the duct retains it quite 

 well if the cannula be inserted for 10 mm. or so. The student's difficulty in regard to the 

 small size of the duct is largely obviated by the capillary unnozzled cannula and by not having 

 to tie it in. A student may mistakenly ' clean ' the ducts by dissection proximal to lingualis 

 nerve, thus destroying corda tympani which accompanies the ducts. Even then secretion 

 may be excited by faradizing the ducts near the gland. 



EXERCISE XIII 



In making the preparation to be used by the student the tracheal cannula should be 

 inserted quite low down, e. g. a couple of cm. or so, above the top of the sternmn, and in 

 doing this care should be taken that the recurrent laryngeal nerves, which lie close to and 

 on the trachea, are not included in the ligature which ties the cannula in the trachea The 

 oesophagus at this level lies not only deep to but somewhat on the left side of the trachea. 

 The low insertion of the tracheal cannula gives the student more room for his dissection ; 

 but it has the disadvantage that the the air supplied to the lungs is less moist, and secretion 

 is apt to collect in the air-passage and hamper respiration in the later stages of the exercise. 



Obs. 59, 60. These follow the procedure of Miller and Sherrington [Quart. Jul. of 

 Exp. Fhysiol. vol. ix, p. 147 ; 1915), except that graphic records of the swallowing 

 movements are not taken. Reflex swallowing is one of the earliest reflex reactions to 

 emerge in the decerebrate preparation. 



Obs. 63. The simple stethograph (Miller and Sherrington, ihid.) used is easily applicable 

 to the preparation whatever the position given the latter. 



Obs. 65. For recording the effect of vagus on respiratory movement it is well to 

 ensure that the lever-point remains in contact with the recording-surface over a considerable 

 sweep of its arc, because the excursion of the movements and the height of their base-line 

 may vary considerably during the observations. 



EXERCISE XIV 



Obs. 68. In the cat the depressor branch of the vagus is usually less separate from the 

 main trunk than in the rabbit. According to some descriptions the depressor runs a more 

 separate course on the left side than on the right, but my own experience has hardly borne 

 that out. In getting ready the preparation for decerebration before giving it out to the 



