76 PRACTICAL HISTOLOGY. 



the thickness of which depends upon the depth to 

 which the canuhi was inserted. If it does not 

 appear thin enough a second attempt should be made 

 at another spot. Then, before the bulk has time to 

 subside that is to say, before the fluid has time to 

 diffuse itself through the meshes of the tissue snip 

 off the whole projection with a single cut of a pair 

 of scissors, which for this purpose should be particu- 

 larly sharp and clean, and transfer the snipped- oft' 

 portion to a clean slide. Here it may either be at 

 once covered in salt solution and examined without 

 reagents, or may be treated with acetic acid, logwood, 

 &c., as in the mode of preparation just described. 



Preparation 6. A modification of the above 

 method consists in injecting into the tissue a solu- 

 tion of gelatine instead of a salt solution. The gela- 

 tine solution is made by taking some very clear 

 French gelatine, allowing it to soak for an hour in 

 water, and then, after pouring off' all the excess of 

 that fluid, placing the soaked gelatine in a beaker 

 over a water bath until it is entirely melted in the 

 water which it had imbibed. The syringe is then 

 warmed by immersing it for a minute or two in 

 warm water, and is filled with the gelatine solution, 

 and a little of this is injected into the subcutaneous 

 connective tissue, so as to produce a bulla like that 

 made by the salt solution. In cold weather the 

 gelatine will set almost immediately ; in warm 

 weather the process may be accelerated by surround- 

 ing the bulla with small lumps of ice. 



When the gelatine is quite firm sections of it are 

 to be made with a razor. As they are cut they may 

 be placed in salt solution. 



Before mounting them it is well to stain the 

 specimens, and one of the best staining fluids for 

 the purpose is a watery solution of magenta. This 

 colors the elastic fibres strongly, the corpuscles dis- 

 tinctly, and the bundles of white fibrils slightly, 

 while the gelatine which was injected and of course 

 occupies all the interstices is hardly stained at all. 



