82 SPECIFIC EXAMPLES OF SLIDE-MAKING 



30 to 40° C, while the lamp above should under no circumstances raise the 

 surface temperature of the material above 60° C. These temperatures are for a 

 moderately dry moss sample and may be exceeded greatly when one is dealing 

 with dry material, such as straw. Wet moss of the sphagnum type, however, 

 requires lower temperatures if it is to be examined successfully. 



If permanent mounts are to be made for record purposes of all the small 

 invertebrates which may be found in the moss sample, it is necessary to make 

 adequate preparations to receive the animals while the moss is being treated. 

 Two kinds of gum mountants are desirable: (1) A high refractive-index 

 medium like Berlese' for the very heavy-walled forms, such as the Oribatid 

 mites and the pseudoscorpions and (2) a low refractive-index mountant like 

 Gray and Wess', for the thinner-walled forms, such as the Tyroglyphid and 

 Gamasid mites. This last medium is also suitable for Thysanura and for Col- 

 lembola. Thick-walled beetles and fleas, if they are to be made into microscope 

 slides, had better be treated with alkali and should be accumulated for this 

 purpose in a tube of 96 per cent alcohol. This process is described in detail in 

 Gray's Microtechnique. It consists usually of soaking the specimens after 

 rehydration in 10 per cent potassium hydroxide. Excessive swelling may be 

 controlled by enlarging the anus with a needle and by putting holes in 

 unimportant parts of the head and thorax. 



If one is dealing with a sphagnum moss, it is also possible that a number 

 of crustaceans, particularly Cladocera and Ostracoda, are likely to be found. 

 These are better mounted in glycerin jelly in the manner also described in 

 Gray's Microtechnique and should be transferred, as soon as they are found, to 

 30 per cent alcohol where they will die with their appendages extended. They 

 should not be permitted to remain in this weak alcohol for longer than is nec- 

 essary to kill them. Then they should be transferred to 96 per cent alcohol. 

 A large number of nematode worms are likely to turn up; these cannot be 

 mounted by any of the methods described in this book, and again reference 

 should be made to the author's larger work. A tube of some fixative, 

 a supply of clean 3- by 1-in. glass slides, and a number of coverslips should be 

 provided to receive any small annelids which may be found in the moss, and 

 . which must be fixed, stained, and mounted at once. 



When all is ready and observation shows that no more forms are falling 

 through the Berlese funnel, the collecting tube beneath it is inspected to see 

 roughly what one has gathered. If there are a great number of Gamasid mites 

 or active insects, it is necessary to open gently a portion of the tube by push- 

 ing away the modeling clay with the thumb and to let a minute drop of ether 



