CIRCULATION OF THE BLOOD. 371 



every kind of organization in a small compass. The following 

 method of preparing this organ for examination under the 

 microscope, without endangering the life of the animal, and 

 which can be repeated a great number of times in the 

 same frog, has been extracted from the London Physiological 

 Journal, page 125, being a modification of that recommended 

 by Dr, Waller : — " A piece of cork, from two to three inches 

 in breadth, and six to eight inches in length, is to be procured, 

 in which is to be bored a hole of about half-an-inch in 

 diameter midway between the sides, and about an inch-and- 

 a-half to two inches from one of its ends. In this part the 

 piece of cork should be of double thickness, which Is effected 

 by joining, by means of marine-glue, a small piece of cork 

 upon the first piece. Upon this is laid the frog, previously 

 enveloped In a Hnen band, or fixed to the cork by pins 

 thrust through the four extremities, so as to prevent any 

 great movements of its body or its feet ; it Is placed 

 upon the back, the end of the nose abutting on the border 

 of the hole. The tongue, the free end of which Is directed 

 backwards, is then to be drawn out of the mouth gently with 

 a forceps, and slightly stretched and elongated until it reaches 

 a little beyond the opposite edge of the hole, where It Is to be 

 fastened by two pins ; the sides are to be fastened over the 

 hole in a similar way. In this state, the tongue presents the 

 appearance of a semi-transparent membrane, which permits us 

 to see through Its substance ; and when placed between the 

 light and the object-glass of the microscope, offers one of the 

 most beautiful and marvellous spectacles which can possibly 

 be witnessed." The other parts of the „ frog In which the 

 circulation can be viewed, are the lungs and the mesentery ; 

 but for both these the abdominal cavity must be opened. In 

 many of the works of the old microscopists, especially Adams 

 and Ledermuller, are shown various contrivances for exhibit- 

 ing the circulation In the mesentery ; the microscope of 

 Lleberkuhn, described at page 17, was contrived for this 

 purpose, and for such was employed by Ledermuller. The 

 plan now generally adopted is to dip the frog into water at 

 the temperature of 120", whereby all muscular action is 

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