262 THE AMERICAN MONTHLY [Sept. 



thorax of a rat or of a rabbit and let the animal die by 

 asphyxia. By the tracliea inject a 1 to 300 solution of 

 silver nitrate so as slightly to distend the lungs. Ex- 

 pose to the sun till opalescent, remove the solution and 

 lightly press the organs. Expand the lungs through the 

 trachea (by the breath), ligate, and suspend the dis- 

 tended org'ans in a dry place. After 24 or 48 hours of 

 drying, section parallel with the surface and mount in 

 balsam 



Preparations described for the study of the capillary 

 circulation and of the endothelium of the arteries should 

 not be neglected. 



Natural I^ijection. — .... Open a living frog, so as 

 to expose the lungs, and in a few minutes, when the or- 

 gan is conjested, put a ligature around the base and place 

 the distended organ in 2 per cent bichromate. In 24 

 hours slit open the lung, leave it for a few hours longer 

 in the fixative, then carefully extend it on a slide, inner 

 surface upward. Stain by haematoxylin and eosine ; 

 mount in balsam 



Injection by Colored Mass. — The soluble Prussian blue 

 mass is to be preferred. Inject by the pulmonary artery 

 and treat like other similarly injected specimens. 



Urinary Organs. 



The Kidney. — The technique of the kidney presents 

 difficulties so that we must make several preparations to 

 show separately the constitution of the numerous ele- 

 ments entering into the composition of the organ. After 

 studying the technique applicable to sections of the renal 

 tissue, we shall study the epithelium of the convoUited 

 tubes, the structure of the glomerule, the intertubular 

 spaces, and the methods of injecting the uriniferous 

 tubes and the blood vessels. 



Sections. — We advise against the use of alcohol as a 

 fixative, as it produces alterations and prevents staining. 



