n PRACTICAL DIRECTIONS 31 



of control, serving to direct or control the actions of the 

 body : the skin, nose, eye, and ear, sensory organs, by 

 which communications are kept up with the external 

 world. 



Tissues. Notice also that the various organs of the 

 body are built up of different materials, or tissues as they 

 are called. We have already distinguished muscle, bone, 

 cartilage, connective-tissue and nervous tissue. Other 

 tissues we shall meet with in the course of a more care- 

 ful examination. 



PRACTICAL DIRECTIONS 



To Kill a Frog for Dissection. Place a frog on a plate, 

 and cover it with a tumbler, or put it into a stoppered bottle. 

 Soak a little bit of cotton- wool or sponge in chloroform, and 

 push it under the edge of the tumbler, or drop it into the 

 bottle. In a few minutes the vapour will make the animal 

 quite insensible, and a somewhat longer exposure will kill 

 it painlessly. 



External Characters. Observe the voluntary and the 

 involuntary respirator}' movements of the living animal, and 

 compare with a dead 'frog when making out the external 

 characters (pp. 4-8) and the position of the various parts 

 of the skeleton (p. 16). 



Sketch the entire animal from the side or from above. 



The Cavity of the Mouth. Gently open the mouth of 

 a dead frog as wide as possible, and make out the points 

 described on p. 17. Sketch. 



The Body-wall. Lay the frog on its back in the dissect- 

 ing-dish, and fix it firmly by sticking pins through the skin 

 of the arms and legs. With the forceps, held in the left 

 hand, pinch up the skin of the abdomen near the middle 

 line between the thighs, and make a nick in it with the 

 point of the scissors. Then, holding the edge of the hole 

 thus made with the forceps, pass in a probe and push it 

 forwards as far as it will go without opposition. Note : 



The sub-cutaneous lymph-sinuses, and the underlying 

 muscle. 



