696 MEDICAL ENTOMOLOGY 



Demodex bovis, Stiles, has been recorded from the skin of cattle in 

 the United States ; it also causes small tumours which become abscesses 

 and often damage the hide. 



COLLECTION AND PRESERVATION 



Mites which are parasitic on small rodents, such as rats and squirrels, 

 may be collected and their life histories studied by placing the animal in 

 a wire rat trap and surrounding it with a cloth as described for fleas. 

 The female mite always leaves its host to lay its eggs, and these may be 

 collected from the cloth. By combing the hair of the host numbers 

 of the immature stages may be collected ; the mites which live on the 

 blood of birds may be studied in the same way. Many snakes and 

 lizards harbour acari, and these are often found below the scales or 

 attached to the cornea. They should be picked up with a moistened 

 brush, never with forceps, and placed in seventy per cent alcohol. Mites 

 which attack insects should either be preserved along with the insect 

 to which they are attached or scraped off with a fine knife and pre- 

 served separately. 



The various free-living forms may be collected by drawing a net 

 over leaves and grass, by turning up old heaps of manure, decaying barks 

 of trees, and stones ; when attached to a plant the leaf or twig should be 

 cut off and the whole placed in spirit. 



Mites can be readily examined in the fresh condition by placing them 

 in a small drop of distilled water on a slide, and covering it with a 



. coverslip ; as the water evaporates it can be replen- 



Examination and . , r 



dissection isned by means of a pipette. In this way it is often 



possible to identify specimens without having to make 

 a cleared preparation. This is, however, necessary when closely allied 

 species have to be separated. Mites are difficult to dissect, but it is often 

 possible to remove most of the organs by placing the specimen in a drop 

 of saline solution on a slide and nicking the integument with a fine 

 needle. Sections are difficult to obtain and double embedding is 

 imperative. 



LITERATURE 



BANKS, N. A treatise on the Acarina or Mites. Proceedings of 



the United States National Museum, Vol. xxviii. 

 1904. Washington. A most useful short account of 

 the Acari. Mr. Banks informs one of the authors in a 

 private communication that a new and revised edition 

 is now in the press. 



