168 



THE ART OF MAKING MICROSCOPE SLIDES 



Rabbit kidney 



is now aiDplied with the mouth, while one 

 watches the stream of sahne coming out of 

 the end to make sure that it is going into 

 the ventricle. If the needle does not lie in 

 the ventricle it may be withdrawn and a 

 further stab made. A skilled operator can 

 stab so as to bring the aperture of the 

 needle into the ventricle nine out of ten 

 times; this is the only skill which is re- 

 quired in the whole operation. As soon as 

 the tip of the needle is seen to lie in the 

 right place, blow very gently until a small 

 quantity of India ink enters the hearts 

 Even though the heart has stopped beat- 

 ing it will now usually start again under 

 the action of the foreign substance in- 

 serted. Continue to blow gently so as to 

 keep the ventricle at all times filled with 

 India ink. It is practically impossible to 

 inject into the blood vessels of the chick 

 bj- pressure; one is forced to rely on the 

 movements of the heart to drive the mate- 

 rial round. If the ventricle is filled with 

 India ink and emptied by contraction a 



half-dozen times, the injection will be 

 found to be perfectly satisfactory, even to 

 the tip of the finest arteries. 



The injection of the veins is slightly 

 more difficult, since it must be undertaken 

 by pressure and in this case the tip of the 

 needle is inserted exactly into the junction 

 of the anterior and posterior cardinal 

 sinuses with the Cuverian sinus. In this 

 case, as soon as the needle is in position, 

 blow with a gentle continuous pressure, 

 watching the other parts of the embryo, 

 and cease instantl_y when the India ink 

 has distributed itself to the ends of the 

 veins. A really successful preparation will 

 fill most of the veins as well as the arteries 

 b}' injection through the ventricle. 



Now remove the needle and drop a 

 small quantity of the selected fixative 

 onto the embryo. If this is done rapidly 

 there will be no leakage of India ink from 

 the tip of the ventricle, and the injection 

 may then be turned into a wholemount by 

 any of the methods described in Chapter 6. 



Precipitation of Lead Chromate in the Glomeruli of a Rabbit Kidney 



This is a preparation of great difficulty, 

 not lightly to be undertaken by the in- 

 experienced, but of which the beauty more 

 than justifies the effort. 



The method requires three solutions, 

 each in the quantity of several hundred 

 milliliters. The first solution is a phj-sio- 

 logical saline which has been saturated, by 

 shaking, with amyl nitrite. Amyl nitrite is 

 a vasodilator of great strength and should 

 be handled carefully. The second solution 

 is a 2% solution of potassium or sodium 

 dichromate, and the third is a 2% solution 

 of lead acetate. All three of these solutions 

 should be passed through a filter immedi- 

 ately before use. There are also required 

 three aspirator bottles, with tubes and 

 glass tips set up in the manner shown in 

 Fig. 87. Lastly a hypodermic needle will be 

 required, with a silk ridge raised on it in 

 the manner described above, and with a 

 diameter approximately two-thirds that 

 of the renal artery of a rabbit. It is also 

 necessary to have a dish of such a depth 

 that the kidney may be covered with 

 physiological saline. 



Now kill the rabbit, preferably with the 

 aid of ether to which has been added a 



considerable quantity of amyl nitrite. 

 Ether produces unconsciousness quickly 

 but death very slowly, and great care 

 should be taken that the rabbit is com- 

 pletely dead before proceeding further. 



Stretch the rabbit on a board, open the 

 abdomen, push the intestines to one side 

 to expose the kidney, and then carefully 

 trace the course both of the renal artery 

 and of the renal vein. These two are then 

 ligated in two places with surgical silk 

 and severed between the ligatures. Now 

 dissect out the rest of the kidney until it 

 is free from the body. It is far more impor- 

 tant that the surface of the kidney should 

 not be damaged than that it should be 

 free of adherent tissues. Remove the 

 kidney from the rabbit and transfer it to 

 a dish of physiological sahne, which is 

 then placed under a binocular chssecting 

 microscope. Insert the hypodermic needle 

 into the renal artery and tie it firmly in 

 place. Take care that the hypodermic 

 needle is entirely filled with saline and 

 that no air entei's. This is why it is desir- 

 able to. work under the sui'face of saline. 



An aspirator bottle filled with amyl- 

 nitrite-saturated saUne is now arranged as 



