218 MANUAL OF HISTOLOGY. 



into the vein. Not more than 5 c.c. should be injected at one 

 time. If the animal be a white rabbit, the result of the first 

 injection shows itself in a 'few seconds, for the animal soon 

 becomes quite blue. After five or ten minutes another 5 c.c. 

 of the solution may be injected, and so on until 20 to 50 c.c. of 

 indigo-carmine solution have been employed, the amount 

 varying according to the size of the animal. 



The excretion of blue 'urine takes place soon after the first 

 injection of indigo-carmine. As soon as a sufficient quantity 

 has been excreted the animal is killed in the following manner : 

 The abdomen is opened and the descending aorta looked for ; 

 when found, the canula of a syringe, filled with absolute alcohol, 

 is attached. The jugular vein is now cut across, and while 

 the animal bleeds to death absolute alcohol is injected up the 

 aorta or into the renal arteries. A safer and better way is to 

 inject the renal artery at once with absolute alcohol ; in either 

 case the renal veins should be cut across. The kidney is at 

 once removed, placed in absolute alcohol, and then divided 

 into several pieces, to insure a rapid action of the spirit. 

 While the indigo -carmine is being injected into the jugular 

 vein, the animal should be wrapped up in flannel or cotton- 

 batting so as to be kept warm. No air should be allowed to 

 enter the vein, or the animal may die before the experiment is 

 concluded. Injection of absolute alcohol through the renal 

 artery should be accomplished before the animal has bled to 

 death, or, at least, immediately afterward. When the kidney 

 has been thoroughly hardened, vertical and transverse sections 

 are to be made through the cortical and medullary substances, 

 and examined in glycerine saturated in chloride of potassium ; 

 or, better still, in resinous turpentine. 



If the injection of absolute alcohol be delayed, either through lack of skill in 

 the experimenter, or any mishap, the indigo salt within the kidney becomes 

 diffused over the entire organ by absorption of water from the contained ves- 

 sels, and the whole kidney becomes of a uniform blue color. Such glands 

 must be laid aside, for sections made therefrom, even after immersion in abso- 

 lute alcohol, are worthless, and will only confuse the microscopist. The abso- 

 lute alcohol of the shops is not always absolute, as is well known. It has a 

 great affinity for water, and, in handling, rapidly absorbs moisture from the air. 

 To make it absolute, I heat sulphate of copper (pure) at a low red-heat. This 

 drives out the water of crystallization, and changes the color from blue to 

 white. Of this I mix a large spoonful or more, while still hot, with a pint of 

 the so-called absolute alcohol, and tightly cork the vessel, which is then to be 



