CIRCULATION OF THE BLOOD. 



80. In fine, the red corpuscles, after having been fully developed 

 in the circulation, are dissolved, and being converted into the 

 fibrinous fluid, pass into the other parts of the organisation, so as 

 to form the different organs of the system. 



81. Next to the constitution of the blood, no subject con- 

 nected with it is more interesting and important than its circula- 

 tion, and we know no spectacle presented by any of the scientific 

 artifices, by which the secret operations of nature are disclosed 

 to our view, which excites more astonishment and admiration 

 than the circulation of the blood, as rendered visible with the 

 microscope. 



82. Let any one imagine an animal organ, full of every variety 

 of blood-vessels of the most complex structure, into the composi- 

 tion of which enter every form of organ : arteries, veins, capillaries, 

 muscles, nerves, glands, and membranes : representing in short a 

 microcosm of the whole animal organisation ; and let us suppose this 

 brought within the field of the microscope, so as to display, before 

 the wondering view of the observer, all the complicated motions 

 and operations of which it is the theatre. Such a spectacle is 

 presented by the tongue of the frog, an object first submitted to 

 this species of experiment by Dr. Donne, at the suggestion of a 

 young Englishman, a Mr., since Dr., Waller, who was in at- 

 tendance upon his course. The method of accomplishing this, 

 with some modifications, as described in the Physiological Journal, 

 is as follows: "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 linen 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-trans- 

 parent 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. It will be found most 



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