237 



or seven di-achms' weight perfectly motionless for twelve hours. 

 The drug does not produce its effect fully for one-and-a-half 

 or two hours. 



Woorali may he obtained from Messrs. Morson & Son, of 

 Sou than', ptori llow. 



The frog having been narcotised by one of these drugs, 

 the circulation may be studied in any of the following struc- 

 tures : — 



(a) The foot-web, which is very familiar to every one, but 

 •which, from its comparative opacity, is useless in observations 

 requiring much nicety. 



(b) The Mesentery. — A longitudinal incision f rds of an inch 

 in length, is made through the skin and muscle of the abdomi- 

 nal Avail, on the left of the middle line ; bleeding is easily 

 arrested by a gentle touch of the solid nitrate of silver. A loop 

 of gut is carefully withdrawn by a pair of photographer's horn 

 forceps, (if the ordinary metal forceps be used, it is most 

 difficult to avoid injury to the delicate vessels on the surface of 

 the gut) . 



Great care must be taken to avoid a tear of the mesentery. 



A tin plate should be prepared, about the size of the stage 

 of the microscoj^e, and having a circular aperture in its centre 

 half an inch in diameter. A ring of cork -] inch in thickness, 

 is glued round the margin of this aperture. The frog is 

 placed on its side, on that part of the plate Avhich is remote 

 from the pillar of the microscope, and the mesentery is laid on 

 the perforated cork. It is a great convenience to have two 

 little arms, one inch in breadth and two in length, projecting 

 from the corners of the plate, on its farther side ; these can be 

 folded over the body of the frog : it is thus held quite steady, 

 and there is no fear of the mesentery becoming displaced. 



The plate may be easily made from an old biscuit box, by 

 means of a stout pair of scissors. A piece of talc is more con- 

 venient than a thin glass, as a cover ; it can be cut to any 

 shape, and is less liable than glass to tear the vessels. The 

 above is a modification of the mode recommended by Professor 

 Cohnheim. Virchow's ^ Archiv,' xl, i, p. 28. 



Woorali is preferable to chloral in this instance. 



(c) The Tongue. — The frog is placed prone or supine, the 

 tongue withdrawn by means of the horn forceps, and stretched 

 to the requisite degree of thinness, over a large perforated 

 cork. The tongue is apt to become dry, and should be 

 moistened with a natural or artificial serum : a mixture of 

 water 100, common salt 1, and albumen 10 parts, has been 

 recommended, and answers well. 



{d) The Lung. — The frog being narcotised as before, is laid 



