The saline solution in which insects are dissected should be kept care- 

 fully, as it forms an admirable medium for the growth of moulds and 



other organisms, the presence of which may lead to 



c , ^i r Saline Solution 



contusion when examining the tissues for parasites. 



It is convenient to have it put up in small quantities in test tubes, each 

 tube sufficing for one lot of dissections, any left over being discarded. 

 When working away from a laboratory it may be carried in small 

 capsules such as are used for bacterial vaccines*; when stored in this 

 manner it will, of course, remain sterile for any length of time, and the 

 capsules are not easily broken. 



The salt solution usually employed is '05 per cent sodium chloride. 

 For ordinary purposes tjiere is no special disadvantage in using the 

 ordinary '075 per cent solution. 



As regards the actual dissection, the method to be employed differs so 

 much according to circumstances that no general description can be given. 

 First and foremost, one should always determine before- 

 hand exactly what one intends to get out of any given Di88ection of fpesh 



specimens 

 specimen, and cut away ruthlessly at everything else. 



Unless material is very scanty, it is. a waste of time to endeavour to 

 dissect out the whole of the internal structures from one specimen. 

 The. more rapidly a dissection is completed the better, especially in dealing 

 with parasites, for it must be remembered that even the salt solution is 

 an unnatural environment for living cells, and it is possible that parasites 

 may change their form in it, though moderately prolonged immersion 

 does not appear to affect the staining properties of the tissue cells. 



The working out of a satisfactory method of dissection in any given 

 case depends upon a knowledge of the anatomy, and particularly of the 

 relations of the internal parts to the exo-skeleton. The alimentary canal, 

 for instance, is attached to the exo-skeleton only at the mouth and at the 

 anus, and is elsewhere only connected with it by the tracheae ; the 

 reproductive organs are connected with the integument only at the 

 external opening ; the salivary glands lie in the thorax, and may extend 

 to the abdomen, the common duct from the two glands passing through 

 the neck. By freeing the portion of the integument to which the system 

 is attached it is possible to draw it out of the body cavity, severing the 

 tracheae as they appear. All the organs will stand a certain amount of 

 pulling, and as a rule the tracheae will break before the softer tissues. 



* Details of the method of preparing and filling such capsules will be found in Sir A. E. 

 Wright's book, The Technique of the Teat and Capillary Tube. 



