602 INVERTEBRATES 



See also Rosenstadt, Arch. mik. Anat., xlvii, 1896, p. 478 ; 

 ViALLANES, Ann. Sci. Nat., xiii, 1892, p. 354 ; and Dietrich, 

 Zeit. rviss. Zool., xcii, 1909, p. 465 (fixes in alcoholic formol, and 

 bleaches with dilute aqua regia). 



1194. Ixodidae, etc. The examination of ticks is unusually difficult, 

 not only on account of their exoskeleton, but also because of variable 

 degrees of distension with blood. It is best to strip off the chitin after 

 a few hours' preliminary fixation in formalin or Regaud's fluid, which 

 makes the underlying tissues firmer and prevents needless injury. 

 Sometimes it is better to delay until dehydration has been commenced. 

 Prolonged action of alcohol makes the chitin more than ever brittle. 

 Another method with nymphs or adults engorged with blood is to 

 squeeze the viscera out through a small opening in the exoskeleton. A 

 pair of artery clamps is better than ordinary forceps, because with them 

 the pressure can be regulated and maintained. With a clean, wet needle, 

 the viscera can be freed as a single drop which keeps its shape as it falls 

 in the fixative. For this purpose Regaud's fluid gives poor results as 

 compared with Zenker's fluid, Giemsa's sublimate, and sublimate acetic, 

 because in it the tissue tends to disperse instead of retaining its spherical 

 shape. For staining, Giemsa's method is suggested (Cowdry, Journ. 

 Exp. Med., xlii, 1925, 257). For the technique of dissecting ticks see 

 Wolbach (Journ. Med. Res., xli, 1919, 67). Useful suggestions for the 

 recognition of Rickettsiae, Giemsa artifact and insect granules in the 

 tissues of blood-feeding arthropods are given by Hertig and Wolbach 

 {Journ. Med. Res., xliv, 1924, 333). 



VERMES 



1195. Chaetopoda : Cleansing Intestine. Kijkenthal {Journ. 

 Roy. Mic. Soc, 1888, p. 1044) puts Lumhrkus into a glass vessel 

 filled with bits of moistened blotting paper. They gradually 

 evacuate the earthy particles from the gut, and fill it instead with 

 paper. 



VoGT and Yung {Traite d'Anat. Comp. Prat., v) recommend 

 coffee-grounds instead of paper, as they cut better after imbedding. 



Joest {Arch. Entwicklungsniech., v, 1897, p. 425) simply keeps 

 the worms for a few days in moist linen, and finds the gut empty. 



Pearl {Journ. appl. Mic, iii, 1901, p. 680) injects alcohol of 

 6 per cent, through the gut of narcotised worms. 



1196. Chaetopoda : Fixation. Lumhricus may be anaesthetised 

 by putting the animals into water with a few drops of chloroform. 

 Perrier puts them into water in a shallow dish, sets up a watch- 

 glass with chloroform in the corner of it, and covers the whole. 



Cerfontaine {Arch, de Biol, x, 1890, p. 327) injects inter- 

 stitially about 2 c.c. of a 1 : 500 solution of curare. 



Jaquet {Bib. Anat., iii, 1895, p. 32) kills Lumhricus in extension 

 in 1 part of nitric acid to 125 of water. 



Collin {Zeit. rviss. Zool, xlvi, 1888, p. 474) puts Criodrilus 

 lacuum into a closed vessel with a little water, and hangs up in 

 it a strip of blotting paper soaked in chloroform. Kukenthal 



