176 THE MICROSCOPE 



Rat, Mouse, or Frog.— Inject from the aorta. 



Injecting Insects.— Insects may be injected by forcing the 

 fluid into the general abdominal cavity, whence it passes into the 

 dorsal vessel, and is afterwards distributed to the system. The 

 superfluous injection is then washed away, and such parts of the 

 body as may be required removed for examination. Insects 

 should be injected very soon after they have emerged from the 

 pupa. The water vascular apparatus, vessels, and the digestive 

 tube may be injected. In some cases the best results are obtained 

 with size coloured with transparent colouring matter; in others by 

 injecting Prussian blue or carmine fluid made with glycerine. In 

 injecting the digestive apparatus of some entozoa, as liver fluke 

 {Distoma, or Fasciola /iepattcu?n), the pipe may be tied in ; but I 

 only make an opening into the vessel and insert the pipe, which 

 must be held steadily while the injection is carefully forced from 

 the orifice. 



Injecting Mollusca (slug, oyster, snail, etc.). — The tenuity of 

 the vessels of many mollusca renders it undesirable to tie the pipe 

 in them. The capillaries are, however, very large, so the injection 

 runs readily. In different parts of the bodies of these animals are 

 numerous lacunae, which communicate directly with the vessels. 

 If an opening be made through the integument of the muscular 

 foot of the snail, a pipe inserted, and the lacunre filled easily, the 

 large vessels of the branchiae may be readily injected with the aid 

 of a pipe having an orifice at the point. 



Injecting Snails (Robertson's plan).— Kill the snails by drown- 

 ing them in a jar quite filled with cold water, the mouth closed 

 with a piece of plate glass. The vascular system is to be injected 

 from the ventricle of the heart with size and carmine. The heart 

 of a snail is easily found. It is enclosed in a sac, which is situated 

 at the posterior extremity of the pulmonary chamber on the left 

 side. The position of the organs of a snail has been fully des- 

 cribed by Dr. Lawson in the Microscopical Joitrnal iox 1863. The 

 injection, introduced into the heart, passes right round the body 

 and returns to the pulmonary chamber. By this plan the arterial 



