122 VASCULAR SYSTEM. 



(7, the intestine can be easily turned over on to b. The intes- 

 tine then lies in the trough c, while the mesentery rests on the 

 glass plate b. So much of the intestine as does not occupy the 

 trough must be replaced. If the observation is prolonged (as 

 in researches on inflammation), it is well to place in the trough, 

 outside of the intestine, a layer of filter paper, on which half 

 per cent, solution of salt is dropped from time to time. It is 

 sometimes useful, when high powers are to be employed, to 

 cover the mesenteiy with thin glass. If the cork is used, it is 

 necessary to fix the intestine at two or three points with small 

 pins. 



Tongue. The animal must be curarized as before. A plate 

 of glass, like that used for the web, is employed, with this 

 difference, that the cork, instead of having a round aperture, 

 is cut into the form of a horseshoe, the convexity of which is 

 towards the edge of the plate. If it is intended to study the 

 circulation on the lower surface of the tongue, the animal is 

 placed on its belly. If the papillary surface is to be examined, 

 it must be on its back. In either case, the tongue must be 

 drawn out by the cornua, around each of which a thread must 

 be secured. With the aid of these threads the organ is drawn 

 as forward as possible without affecting the circulation, and 

 secured to pins which are stuck horizontally into the edge of 

 the cork at each corner. It is sometimes necessary to extend 

 the organ further by means of pins stuck in the cork at the 

 sides. 



Tail of the Tadpole. The tail of the tadpole affords a 

 most instructive object. The animal is curarized by placing 

 it in a drop or two of solution in a watch glass. As soon as 

 it is motionless it is transferred to an object-glass and ex- 

 amined. The description of the phenomena of circulation as 

 seen in the batrachians, and of the methods employed for their 

 investigation in mammalia, will be found in Chapter XVII. 



Observation of the Emigration of Colored and 

 Colorless Blood Corpuscles. In the tadpole, emigration, 

 particularly of the colored corpuscles, may be witnessed in 

 various parts of the tail, if the observation is continued for 

 a short time. 1 If the mescnte^ of a frog is exposed to the 

 air, or treated with any irritant, the emigration of colorless 

 corpuscles can be seen with the greatest ease, provided that 

 the observation is made with sufficient care. A small vein 

 must be sought out with a low power, and a point selected in 

 its course at which one or more colorless corpuscles have 

 attached themselves to the walls. These must then be watched 

 continuously under a higher power. 



1 In the frog an abundant emigration of colored corpuscles takes 

 place after the injection of salt solution (two to six per cent,). 



