AMMONIA. 



[ 29 ] 



AMPHILEPTUS. 



which each alternate crystal will become 

 black, the intermediate ones appearing 

 coloured; and on continuing the rotation, 

 the crystals which were at first black will 

 appear coloured, those which were coloured 

 appearing black. 



The blackness of the crystals arises from 

 the plane of primitive polarization of the 

 light transmitted by the polarizer being 

 parallel with the optic or neutral axis of the 

 crystals, consequently there is no double 

 refraction and no interference to produce 

 colour ; whilst in the coloured crystals, the 

 optic axis of .which does not coincide with 

 the plane of polarization, double refraction 

 and interference ensue, by which the colours 

 are produced. The tint of colour varies 

 according to the thickness of the disks. 



See CIRCULAR CRYSTALS and POLARI- 

 ZATION. 



AMMONIA, PURPURATE OF; also called 

 Murexide. Is an artificial product of the 

 decomposition of uric acid. It may be pre- 

 pared by dissolving uric acid in dilute nitric 

 acid, as directed under AMMONIA, OXALU- 

 RATE OF. The solution is evaporated 

 until it acquires a tile-red colour ; then 

 cooled to exactly 158 Fahr., and dilute so- 

 lution of ammonia added to it, until it is 

 neutralized. Half its bulk of water is then 

 added, and the mixture deposits the salt in 

 crystals as it cools. 



The crystals form short, flattened, four- 

 sided prisms (PI. 7- fig- 10) ; they are ruby- 

 red by transmitted light, and the two broad 

 surfaces are emerald-green by reflected light. 

 They are also analytic. 



BIBL. See CHEMISTRY. 



AMMONIA, URATE OF. See URATES. 



AMMONIO-CHLORIDE OF PLATI- 

 NUM. See PLATINUM. 



AMCEBA, Ehr. (Amiba, Duj.). A genus 

 of Infusoria, of the family Amcebaea. 



Char. The same as that of the family. 



Ehrenberg admits four species ; to these 

 Dujardin has added ten; but the characters 

 cannot be depended upon. 



They are found in almost all infusions 

 which have not become putrid ; also in the 

 slimy debris covering bodies immersed in 

 fresh or salt water. 



Their size varies from 1-70 to 1-2800". 



Amoeba diffluens (aquatic) is represented 

 in the expanded state by PI. 23. fig. 9 a; and 

 when contracted, by fig. 9 b. 



AMCEBA A, Ehr. and Duj. A family of 

 Infusoria. 



Char. Animals composed of a glutinous 



substance, without integument or internal 

 structure, constantly changing form by the 

 protrusion or retraction of parts of the body, 

 whence result variable expansions; move- 

 ment slow r . 



These curious organisms apparently con- 

 stitute the simplest forms of organic beings, 

 for they consist of a single kind of matter, a 

 simple mass of sarcode. When first placed 

 upon a slide, they represent minute rounded 

 semitransparent masses; but soon one or 

 more rounded or pointed lobes, or transparent 

 expansions, are seen to shoot out from the 

 margin. These move almost imperceptibly 

 along the slide, and becoming fixed to it, 

 slowly draw the mass towards the fixed 

 point. They are usually found to contain 

 within them other Infusoria, Diatomaceae, 

 Desmidiacese or other minute Algae serving as 

 food; these bodies being involved in the same 

 manner as occurs in thecaseof ACTINOPHRYS, 

 atemporary digestive cavity beingthus formed. 

 Sometimes also vacuoles are seen within them, 

 containing simply the surrounding liquid; 

 these contract occasionally and disappear. 



They are propagated by spontaneous 

 fission. When cut or torn, each segment 

 contracts upon itself and forms a new being. 



One genus, AMCEBA. See RHIZOPODA. 



AMPELOMYCES, Ces. See OIDIUM. 



AMPHIBLISTRA, Presl. A genus of 

 Pterideae (Polypodaeous Ferns). Exotic. 



AMPHILEPTUS. A genus of Infusoria, 

 of the family Colpodea (Ehr,). 



Char. Eye-spot wanting ; no tongue-like 

 process ; proboscis and tail present. 



The so-called proboscis resembles in ap- 

 pearance a neck. 



Dujardin gives the following characters, 

 placing the genus among his Paramecia. 

 Body elongated, fusiform or lanceolate, nar- 

 rowed at each end, or at least at the anterior 

 extremity, and furnished with an oblique 

 lateral mouth. 



These animals are usually found in clear 

 marsh water, and in streams, between aquatic 

 plants. They are all furnished with cilia but 

 one ; in some these are arranged in longitu- 

 dinal rows. Species : 



1. Amphileptus anser, E. (Dileptus anser, 

 D.). Colourless; length 1-120". 



2. A. margaritifer, E. and D. Colour- 

 less; 1-72". 



3. A. moniliger, E. and D. Colourless ; 

 1-72 to 1-96". 



4. A. viridis, E. and D. Green ; 1-120 to 

 1-4G". 



5. A. fasciola, E. and D. Colourless; 



