AMMONIA. 



AMCEBA. 



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 POLARIZA- 

 TION. 



AMMONIA, PURPURATE OF, or Murex- 

 ide. Is an artificial product of the decom- 

 position of uric acid. It may be prepared 

 by dissolving uric acid in dilute nitric acid, 

 as directed under AMMONIA, OXALURATE 

 OF. The solution is evaporated until it 

 acquires a tile-red colour ; then cooled to 

 exactly 158 Fahr., and dilute solution of 

 ammonia added to it until it is neutralized. 

 Half its bidk 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. 11. fig. 10) ; they are 

 ruby-red by transmitted light, and the two 

 broad surfaces are emerald-green by re- 

 flected light. They are also analytic. 



BIBL. See CHEMISTRY. 



AMMONIA, ITRATE OF. See URATES. 



AMMONIO-CHLORIDE OF PLATINUM. 

 See PLATINUM. 



AMCE'BA, Ehr. A genus of Rhizopoda, 

 of the order Lobosa, and family Amcebaea. 



Char. The same as that of the family j 

 but the psetidopodia of one kind only. 



These curious organisms constitute the 

 simplest forms of animal 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 semi- 

 transparent 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 Infusoria," Diatomacese, Des- 

 midiace?e or other minute Algae which are 

 supposed to serve as food ; these bodies 

 being involved in the same manner as occurs 

 in the case of ACTINOPHRYS, a temporary 

 digestive cavity being thus formed. Some- 

 times vacuoles or contractile vesicles are 

 seen within them, containing simply the 

 surrounding liquid; these contract occa- 

 sionally and disappear. 



Ehrenberg admitted four species ; to these 



Dujardin added ten, and others have since 

 been added ; 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 ; sometimes on moss or 

 earth. 



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



Amoeba diffluem is represented in the ex- 

 panded state by PI. 30. fig. 9 a ; and when 

 contracted, by fig. 9 b ; fresh w r ater. 



A. princeps. Yellowish white, filled with 

 highly refractive granules ; 1-50" in diam. 

 In pools. 



A. blatta, found in the common cock- 

 roach, has the body striated (probably the 

 early stage ofaGregarina). 



Amoeba villosa (Wallich) has one part of 

 the body covered with short processes or 

 villi. 



In many Amcebte, when the pseudopodia 

 are expanded, the margin of the body ap- 

 pears very transparent, while the inner por- 

 tions remain granular ; this has been re- 

 garded as indicating the existence of an 

 endosarc and an exosarc. But when a drop 

 of liq. potassfs is added to an Amoeba, all is 

 dissolved, except the granular matter of the 

 body, which consists of foreign particles, 

 oil-granules, &c. 



Many so-called Amoeba are probably 

 early stages of Fungi, &c. ; but in such 

 simple structureless bodies, nothing can be 

 stated certainly, without the use of chemical 

 tests. 



Certain Amoeba-forms, in which no nu- 

 cleus or vacuoles occur, have been separated 

 by Ha'ckel as MONERA ; but since any de- 

 tached fragment of an Amoeba, or even of 

 any Rhizopod, will live and form a new 

 being, it is evident that such characters are 

 valueless. 



Amoeba-like movements of the sarcode or 

 protoplasm are often perceptible in isolated 

 normal and pathological structures as in 

 the blood-corpuscles, the liver-cells, the 

 corpuscles of dropsical liquids, the embry- 

 onal cells of ova, &c. ; also in various vege- 

 table cells, the root-cells of Chara, Volvox, 

 the spores of Algae, the Myxogastres, &c, 

 Amoeba-like movements may even occur in 

 dead cells (Lieberkiihn). 



An Amoeba with a large cilium and a 

 villous tail has been described by Carter ; 

 and a free swimming Amoeba with a cilium 

 by Tatem. 



BIBL. Ehr. Infus. 126; Dujardin, Inf. 



