170 



THE ART OF MAKING MICROSCOPE SLIDES 



Intestine 



Injection of the Intestinal Capillaries of a Rabbit with Carmine-gelatin 



The capillaries of the intestine may, of 

 course, be injected with lead chromate in 

 the manner described in the last example. 

 This illustration is given, however, for the 

 benefit of those who prefer the more con- 

 ventional method of filling the fine capil- 

 laries with red gelatin for study. 



The same rabbit may be used as was 

 used in the last example provided that 

 there are available two more aspirator 

 bottles, one containing normal saline and 

 the other 4% formaldehyde. While the 

 kidney is being perfused with saline, in 

 the manner described in the last example, 

 remove a length of about two inches from 

 the intestine, including a portion in which 

 a branch of the mesenteric artery is seen 

 to enter the intestine. Now place this in 

 the dish with the kidney and attach it to 

 its own aspirator system of normal saline, 

 after having inserted a hypodermic needle 

 into the artery exactly as described in the 

 case of the kidney. Perfuse this specimen 

 until all the blood has been removed. Now 

 transfer it to another dish and perfuse, 

 after the normal saline, 4% formaldeh3'de. 

 It will be noticed that in this preparation, 

 no precautions have been taken to open 

 a reheving vein; the purpose of the per- 

 fusion \\T.th 4 % formaldehyde is to expand 

 the fine capillaries and permit them to set 

 in this expanded condition. After the per- 

 fusion has gone on for about a couple of 

 hours, remove the piece of intestine and 

 transfer it to a jar of 4% formaldehyde, 

 where it may remain until next required. 



The writer has never found it practical 

 to set up an elaborate arrangement of hot- 

 water baths with a view to injecting fresh 

 material with a gelatin mixture and, there- 

 fore, has alwaj's recommended that the 

 material be fixed and hardened with the 

 capillaries widely expanded. By this means 

 it is possible to secure a specimen which 

 may be injected relatively rapidly with a 

 carmine-gelatin material held in a hypo- 

 dermic sjainge. 



Of the many carmine-gelatin injection 

 media, the formulas for which are given in 

 Chapter 28 under the heading V 32.1, the 

 writer prefers that of Moore 1929. About 

 100 milliliters of the selected mass will be 

 required. 



Before the injection can be made, the 

 formaldehyde must be removed from the 

 specimen. This may be done by washing 

 the specimen for two or three days in 

 running water, though it is usually safer 

 in addition to perfuse it through the 

 needle — which has, of course, remained 

 attached to the artery throughout this 

 period — -using an aspirator system set on a 

 shelf above the sink in which the specimen 

 is being washed. When all of the formalde- 

 hyde has been removed, secure a vessel 

 large enough to hold both hands, a one- or 

 two-milliliter hypodermic syringe, and the 

 specimen. Fill the dish with water heated 

 to about 35°C. before placing in it the 

 kidney and the hypodermic syringe. The 

 temperature is not of importance, pro- 

 vided that it is above the melting point of 

 the gelatin mixture. Melt the gelatin on a 

 water bath and, when the kidney and 

 needle have both been warmed through, 

 remove the hypodermic syringe from the 

 water bath, fill it in the ordinary manner 

 with the injection mass, and then lower it 

 into the water bath and attach it to the 

 hypodermic needle. Now apply a slow and 

 gentle pressure to the end of the plunger 

 until a sufficient quantity of gelatin has 

 been injected into the capillaries. The 

 terminal point of the operation may be 

 judged when reasonably large areas have 

 become bright pink to red in color. Do not 

 expect the injection to go into the whole 

 length of the intestine ; be satisfied if }i of 

 an inch is well injected. 



Now remove the hypodermic syringe 

 and then drop the piece of intestine into 

 ice water in order to chill and set the 

 gelatin. As soon as the kidney is chilled 

 it is transferred back to 10% formalde- 

 hj'de, where it may remain until wanted 

 for the production of sections of about 100 

 microns in thickness. In the present case 

 excellent sections may be prepared by 

 embedding in any low-melting-point wax, 

 and cutting single sections on any kind 

 of microtome. These sections are then 

 attached to the slides by using very 

 considerable quantities of adhesive, be- 

 fore being dewaxed and transferred to 

 balsam in the manner described in 

 Chapter 12. 



