Abstract
The method to be described is a modification of that used by McJunkin 1 which proved to be inapplicable for use on lung tissue. After our technique had been perfected Cash 2 reported a similar method, but ours, we believe, offers certain advantages. Two pathways are employed for injection of the vital stain, either the intratracheal, the intravenous or a combination of the two. In using the former the animal is first killed by air embolism. For the latter method the dye is injected into a vein 10 minutes before its death. In rabbits intravenous injections are made into the ear vein; in guinea pigs, the jugular veins are exposed under local anesthesia with 3 per cent cocaine. Ether cannot be used, as it destroys the capacity of the pulmonary cells to react specifically to the dye.
Supravital Staining—(a) Intratracheal injection: 30 to 40 cc. of a warm 1:1500 solution of neutral red made up in physiological salt solution is injected into the guinea pig's trachea, which is then tied off. The whole animal is incubated at 37° C. for 5 to 30 minutes. After this interval the dye ceases to react specifically and stains the nuclei. (b) Intravenous injection: 60 to 80 cc. of the same solution are slowly injected into the jugular vein or carotid artery of a guinea pig. If the animal survives it is allowed to live 10 minutes before being killed by air embolism. Occasionally it dies and the whole body is incubated as just described.
Fixation—This is accomplished by dropping the lungs and heart into alkaline Zenker-iormol solution. After intravenous staining the lungs are distended with air. To prepare this fixative add sufficient solid NaOH to U. S. P. formaldehyde solution to give a pH value of 7.6.
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