141 



both tissues and included parasites are usually to 

 be obtained by the use of fixed tissues. Several 

 tissues (including the salivary glands and mid- 

 gut) may, when dissected out, be spread by means 

 of the edge of a slide or cover-glass, and rapidly 

 dried. These, fixed and stained, give beautiful 

 preparations of sporozoits, as well as certain 

 parasites in the mid- gut, hind- gut, etc. 



For fixing mosquitoes as a whole, watery 

 solutions are not generally so good as alcohol, on 

 account of the difficulty of penetration from the 

 nature of the exoskeleton and the large amount of 

 air contained in insect tissues ; very good results 

 are obtained by fixing and hardening in abso- 

 lute alcohol, and proceeding at once to embed in 

 paraffin. It is best, so soon as considerable 

 hardening has taken place, to make a minute 

 incision into both the thorax and abdomen. For 

 fixing portions or isolated organs of mosquitoes 

 saturated solution of perchloride has advantages 

 over alcohol and fixes the cells of the mid-gut 

 extremely well. It does not penetrate, however, 

 well into undissected mosquitoes. Picric acid 

 gives good results with isolated organs. The 

 changes in the mid- gut cells during digestion are 

 well shown. 



Both CuUcines and Anophelines, but especially 

 the latter, cut readily in paraffin or celloidin. For 

 staining smear preparations and sections hae- 

 matein gives very good results ; sporocysts and 

 sporozoits, as well as the normal tissues, are well 

 stained. 



The stellate cells in connexion with the 

 tracheal endings upon the mid- gut, etc., are fre- 

 quently well shown by gold chloride (Fig. 32). 



