106 SUMMARY OF CURRENT RESEARCHES RELATING TO 



partly so, whereas crystals are supposed to be essentially solid bodies. 

 This supposition now no longer holds good, for Lehmann and some 

 other chemists have succeeded in producing truly liquid crystals. Of 

 these about fifty varieties have become known up to the present. 

 The first kind discovered consisted of a modification of silver iodide 

 which is stable above 14fi^ C. It is viscous liquid, but under the 

 microscope it reveals a distinctly crystalline structure. The most 

 familiar example is soft soap, which consists of innumerable soft crys- 

 tals. Some new chemical preparations with alarming names show this 

 structure more strikingly. Vorlander's para-azo-oxy-benzoic-ethyl-ester 

 is seen to consist of numerous crystals in constant motion. Whenever 

 two crystals collide they coalesce with a jerk, just like drops of liquid. 

 Another substimce exhibits soft crystals in long straight columns with 

 sharp facets. Gattermann's para-azoSy-phenetol is as liquid as water, 

 and occurs in drops ; but each drop possesses a structure which is easily 

 proved to ])e of a crystalline character. Seen in the direction of the 

 axis of symmetry, each drop appears to have a round nucleus ; but seen 

 in a direction normal to this axis, the nucleus appears like a l)i-convex 

 lens. Both these structures are unreal. They are products of refraction. 

 But they prove that the drops are not isotropic. When two drops collide 

 they form one drop ; but the new drop has two nuclei, with u third 

 between them, and this lasts for several minutes. In polarised light 

 the drops show well-marked dichroism, and between crossed nicols they 

 show beautiful interference colours, just like solid crystals. On squeezing 

 or bending such a liquid crystal and releasing it, it resumes its original 

 shape after a short time, just as an amoeba would do. Two species of 

 crystals may be " crossed ." Thus, two varieties of cholester-ethyl-caprinate 

 may be combined in a structure recalling the lustre of a butterfly's wings. 

 These phenomena, striking as they are, do not exhaust the wonders 

 of liquid crystals. Vorliinder has observed exceedingly curious phe- 

 nomena in a substance called para-azoxy-cinnamo-ethyl-ester. Under 

 suitable conditions, the crystals take the shape of spheres flattened on 

 one side. When two such drops meet three different things may happen. 

 Either the drops are in the same position — say with both bases down- 

 ward, and one on top of the other : then they coalesce into one round 

 drop. Or the bases touch : then they form a twin or couple without 

 running together. When they meet in any other way they form a drop 

 with two flat surfaces. The "copulation" of two individuals has a 

 remarkable counterpart in the process of " budding," which is sometimes 

 observed, small buds appearing on the flat surfaces, and dropping off 

 when they reach a certain size. Further, the drops often make a chain 

 resembling a l)acterium, growing by intussusception instead of by apposi- 

 tion. These rods may be spirals, and are often seen in serpentine motion. 

 Eventually they break up, and each fragment develops into a perfect in- 

 dividual. These curious experiments, which were exhibited at the Congress, 

 made it practically impossible to assign a definite limit to vital phe- 

 nomena, or to say where organic matter ends and inorganic matter 

 begins. 



"to" 



Quekett Microscopical Club. — At the 434th Ordinary Meeting of 

 the Club, held on November 16, 1906, Mr. F. P, Smith communicated 



