158 PRACTICAL HISTOLOGY. 



covering glass nnist be placed over the part of the mem- 

 brane which is to be examined, so as to sink it in the fluid 

 and keep it steady. But in spite of every precaution, the 

 circulation under these conditions retains its normal 

 character but a short while, and inflammatory congestion 

 and stasis, or complete stoppage of the flow of blood, 

 rapidly supervenes. 1 



Preparation 9. Circulation in the lung of the 

 toad. This is readily observed with the aid of the 

 mesentery board. The animal must, as before, be 

 first rendered insensible and curarized, but it will 

 be found that a good-sized toad will require at least 

 six times as much curare as a frog. An opening is 

 made at the side of the chest .large enough to allow 

 the lung, which in the toad almost always remains 

 distended with air, to protrude. The animal is then 

 propped up on the mesentery board (Fig. 26) in such 

 a manner that the lung rests over the aperture ft, 

 and the circulation can be studied in the part which 

 is uppermost without further trouble. A frog may 

 be used in a similar way, but there is much greater 

 difficulty in keeping the lung distended. In either 

 case the greatest care must be taken to avoid prick- 

 ing, or in any way rupturing the wall of the lung. 



Preparation 10. Circulation in the tongue 

 of the toad. By far the most beautiful object for 

 studying not only the circulation but also the tissues 

 in the living animal, is the tongue of the toad, and 

 in a slightly less degree that of the frog. The tongue 

 is in these creatures an extremely extensile organ, 

 which, under ordinary circumstances, lies folded 

 back on the floor of the mouth (Fig. 27, B), but which 

 can at the will of the animal be protruded for a con- 

 siderable distance (c). For the preparation of the 

 organ the cork plate is again necessary ; a smaller 

 piece of cork of the shape shown in the figure (Fig. 



1 For a detailed account of this method the student is referred 

 to the original description by Knrdon Sanderson and Strieker, 

 in the " Quarterly Microscopical Journal" for 1.870. 



