Rabbit kidney 



INJECTIONS 



169 



shown ill Fig. 87, and the ground end of 

 the ghiss conuet'tion inserted into the 

 hypodermic needle. Tliis should be done 

 under the surface of saline in order to 

 avoid an)' possibility of air bubbles. Cut 

 the renal vein above the first ligature and 

 remove the clip froni the rubl)or tul)e 

 leading to the aspirator bottle. A stream 

 of blood will immediately leave the renal 

 vein as it is displaced by the saline being 

 injected into the artery, and the perfusion 

 should be continued until this stream of 

 blood stops. Now replace the clij) on the 

 rubber tube and withdraw the glass con- 

 nection from the hypodermic needle. 

 Change the bloody saline in the dish for 

 clean saline, being careful that at no time 

 does the open end of the hypodermic 

 needle have any opportunity to acquire 

 an air bubble. 



Now take the second aspirator bottle 

 which contains the 2% potassium dichro- 

 mate, remove the clip until a clear stream 

 of chromate is flowing through the glass 

 connection, and then attach the glass con- 

 nection to the hypodermic needle. Open 

 the clip again and allow the potassium 

 dichromate to flow through until it is seen 

 to have rej^laced the saline in its entirety. 

 Replace the chp again, remove the dichro- 

 niate-filled aspirator bottle, and replace 

 the dichromate-contaminated saline in the 

 dish with fresh saline. It is better to re- 

 place it two or three times to be quite 

 certain that no dichromate remains in the 

 dish. Before the last change of saline, 

 briefly connect the aspirator bottle con- 

 taining the saline and the hypodermic 

 needle, and permit the saline to flow for 

 about a couple of seconds to make sure 

 that the hypodermic needle and its con- 

 nections are again rendered free of dichro- 

 mate. If this precaution is not taken, the 

 needle is almost certain to become choked 

 with lead chromate when the lead acetate 

 is injected, and the solution in the dish 

 will become so cloudy that one can no 

 longer see what is going on. 



As soon as there is no potassium dichro- 

 mate anywhere except in the kidney, take 

 the third bottle containing the 2% lead 

 acetate and connect it to the hypodermic 

 needle. Remove the chp and permit the 

 lead acetate to flow until the entire kidney 

 has assumed a dense, opaque yellow ap- 



pearance. It is very improbable that any 

 of the precipitated lead acetate will be 

 forced through the fine capillaries of the 

 glomeruli and out through the renal vein. 

 The time necessary to precipitate the 

 material within the glomeruli of the kid- 

 ney may vary from five minutes to two or 

 three hours but can readily be judged by 

 eye. Even though only certain areas of 

 the kidney go densely opaque yellow, the 

 preparation should not be rejected since 

 many sections may be obtained from even 

 a small, properly injected, area. The kid- 

 ney is now removed from the saline and 

 thrown into 10% formaldehyde until it is 

 next required. 



The kidney will be sufficiently hardened 

 to permit sectioning in about a week. At 

 the end of this time, therefore, the kidney 

 is transferred to a sahne solution and cut 

 into sUces about two millimeters thick. 

 Do not be alarmed that there will be 

 hberated at this time considerable quan- 

 tities of lead dichromate. The lead dichro- 

 mate \v\\\ not come out of the fine capil- 

 laries of the glomeruU, and each slice 

 should be washed until it ceases to give 

 rise to the clouds of yellow pigment which 

 are, by this process, removed from almost 

 all vessels except the finest ones. These 

 two-millimeter slices should now be cut 

 into sections about 100 microns thick 

 (J^o milhmeter). This may be done either 

 bj^ embedding them in a very soft wax in 

 the manner described in Chapter 12, or, far 

 better, by embedding them in nitrocellu- 

 lose in the manner described in Chapter 

 13. Whichever method is adopted, the sec- 

 tions should be mounted in balsam, and 

 the utmost care should be taken to de- 

 hydrate and clear them thoroughly, so 

 that the uninjected tissues appear glass- 

 clear. After they are mounted these sec- 

 tions may be studied by transmitted light, 

 in which case the glomeruli will be seen 

 only as an opaque shadow; or they may 

 be studied by reflected light, either after 

 the slide has been placed on a black back- 

 ground, or after a piece of black paper has 

 been attached to the undersurface. The 

 examination of these specimens by re- 

 flected light will show the relationships of 

 the glomeruli, and their attendant arteri- 

 oles, better than any other method known 

 to the author. 



