170 INJECTING SMALL ANIMALS FOR 



change is not constant. It depends on the strength of the ammonia 

 used, the amount of ammonia which has escaped during the mani- 

 pulations, and also on the strength of the acid. 



The change in colour may be plainly seen, as it is quite marked 

 and sudden, by looking, not into the mouth of the jar, but on its 

 side, where the light is strongest, and when the change in colour 

 comes the gelatin is ready for use ; but it will do no harm to use 

 all the acid prepared. A greater quantity of water with weaker 

 ammonia would do, but it is best to use a standard article. So 

 also with the acid. The ordinary acetic acid would do if we used 

 more of it and waited for the change in colour. If we put in too 

 little acid, the fluid would be too dark, and the colour would pass 

 through the walls of the blood-vessels, staining the intervening 

 tissues. 



For injecting we need the following : — 



I. — Injecting-syringe, with canula and stopcock. 



2. — Curved needle, threaded with No. lo Chinese silk. 



3. — Some ordinary strong parcel twine. 



4. — A sharp-pointed knife. 



5. — An ordinary wash-basin. 



6. — A kettle of hot water. 



7. — A pail of ice water. 



8. — A starch or other box, with sliding lid. 



9. — Some chloroform. 

 We should use much more gelatin solution than would fill the 

 animal's blood-vessels, because a considerable quantity should be 

 allowed to pass through and out of the animal to wash out the 

 remains of the blood, which if left in would turn black ; and also 

 because a greater amount should be forced and left in, to ensure 

 well-filled capillaries in our sections. 



When ready to inject, the jar of gelatin, the syringe, and parts 

 should be kept in warm water. 



The animal should be placed in the box and the lid closed. 

 Next pour some chloroform on a cloth and drop it into the box, 

 and wait for the animal to cease moving about. After narcosis is 

 complete, and before the animal ceases to breathe, it should be 

 removed from the box. The operator should with the thumb and 

 finger seize the skin of the belly to lift the parts from the intes- 



