WITH THE MICROSCOPE. 14! 



Demonstrated in the Lower Animals than in Man and the Higher 

 Animals. In consequence of the great complexity of the structure 

 of many of the tissues of the higher animals, their rapid change after 

 their removal from the body, and their extreme delicacy, anatomists 

 have long been in the habit of resorting to the examination of tex- 

 tures in the lower forms of animal life for obtaining an insight into 

 the structure of parallel tissues in the higher, and with considerable 

 success. I can adduce no better example of the great value of such 

 an appeal to the simpler forms of animal life than occurs in the case 

 of the kidney. 



In animals generally, this gland consists essentially of a vast 

 number of long and highly tortuous tubes which in the higher 

 members of the class are packed so closely together that they form 

 a firm and very compact organ, the general characters of which are 

 familiar to all and of vessels bearing a particular relation to these 

 tubes. In such a kidney it is impossible, under ordinary circum- 

 stances, to follow a tube for any very great length, as the observer 

 will be convinced if he looks at a specimen in the microscope ; but 

 in the lower animals the kidney is less compact, and the several 

 tubes are not so intimately connected together. Indeed, in many 

 of them the kidney is prolonged into a thin, transparent, almost 

 thread-like organ, which extends into the thoracic portion of the 

 animal. In this situation in the common newt or eft (Triton or 

 Lissotriton) we have, so to say, a natural dissection of the elements 

 of the gland structure, and we may demonstrate an arrangement, the 

 existence of which we can only infer by an examination of thin sections 

 of the compact kidney of mammalia. The method of dissection is 

 described in 257 on Ciliary Movement, p. 162. Single tubes, 

 with the structures connected with them, may be traced throughout 

 their entire length, and are quite separate from one another. I need 

 hardly observe, that it would be vain to attempt to make such a 

 dissection artificially. See fig. 218, pi. XXXIII. A probe is placed 

 under this portion of the kidney. If a piece of this be carefully 

 removed from the recently-killed animal, the cilia lining the whole 

 length of the tube will be seen in active vibration. Beautiful speci- 

 mens, showing the continuity of the tube with the flask-like dilatation 

 enclosing the vessels of the tuft, may be obtained from animals 

 which have been injected with the Prussian blue fluid, fig. 219. 



Many other instances of the value of this kind of investigation 

 might be adduced of equal interest and importance, but instead of 

 occupying time in this manner I will most strongly urge upon all 

 those who are likely to prosecute researches upon the characters of 

 any particular tissue or organ, the importance of investigating care- 



